Veterinary Nervous System (Animal)

Nervous System  

Neuron = functional cell of Nervous System:

             — receives excitation (at a synapse or at a receptor);

             — conducts excitation (along an axon);

              transmits excitation (via release of chemical at a       

              synapse).

Most neurons are multipolar  — cell body is located where input

                                                     excitation occurs

Sensory neurons are unipolar — cell body is located along the

                                                     axon 

Definitions:

  Nerve = bundle of axons ensheathed by supporting cells and enveloped by connective tissue,.

  Root = nerve that is adjacent to the CNS and enveloped by meninges

Ganglion = localized site where a nerve is enlarged due to a collection of cell bodies:

        Spinal ganglia — contain unipolar cell bodies (located on

                                      dorsal roots of spinal nn.)

        Autonomic ganglia — contain multipolar cell bodies that

                                             innervate viscera.

Nervous System Divisions:

 Central (CNS): brain  and  spinal cord

  Peripheral (PNS): 12 pairs of cranial nerves (attached to brain);

36 pairs of spinal nerves in the dog & cat (attached to

spinal cord). [8 cervical; 13 thoracic; 7 lumbar; 3 sacral; & 5 caudal]

Spinal Nerve:

The spinal cord and spinal roots are located within the vertebral

canal of the vertebral column. Dorsal and ventral spinal roots unite toform a spinal nerve (bilaterally). Adjacent vertebrae combine to form an intervertebral foramen (dorsal to an intervertebral disc). The spinal nerve is found within theintervertebral foramen, from which it exits the vertebral canal.The spinal nerve is enveloped by connective tissue (epineurium,perineurium, & endoneurium). In contrast, the spinal cord and the dorsal and ventralspinal roots are surrounded by cerebrospinal fluid enclosed within meninges.

Spinal Nerve:  typical pattern

 — short (<1 cm); located at an intervertebral foramen

—   connected to the spinal cord by two roots (each comprised of

      rootlets):

dorsal root — composed of afferent (sensory) axons; the site of a

                        spinal ganglion

ventral root — composed of efferent axons that innervate muscle

                         & gland

                    — divides into four primary branches:

meningeal branch — small; sensory to meninges

ramus communicans — connects to sympathetic trunk & innervates viscera

ventral branch — largest branch; hypaxial mm. & lateral and ventral cutaneous nn.

dorsal branch — medial & lateral branches.; epaxial mm. & dorsal cutaneous nn.

Fiber types:  types of nerve fibers (axons) found in a spinal nerve and its branches

  • Afferent (sensory) — axons associated with receptors and unipolar cell bodies in spinal ganglia

General Somatic Afferent (GSA): receptors in skin & muscles, tendons, joints

General Visceral Afferent GVA): receptors in viscera

  • Efferent (motor) — axons that innervate muscle & gland;

 cell bodies are located in the spinal cord (or in some cases autonomic ganglia)

          Somatic Efferent (SE): innervates skeletal muscle

          Visceral Efferent (VE): innervates cardiac m., smooth m., &         

          gland

Cutaneous innervation:

Neck — series of dorsal and ventral cutaneous nn.

Thorax — series of  dorsal, lateral and ventral cutaneous nn.

Abdomen — series of dorsal and lateral cutaneous nn.

Limbs — individually named cutaneous branches of regional

                nerves thatoriginate from nerve plexuses (brachial or

                lumbosacral) to the limbs.

Face — named cutaneous branches of cranial nerves.

Brachial and Lumbosacral nerve plexuses:

Individual muscles are composed of multiple myotomes that overlap in forming the muscle.In the case of trunk muscles, which are generally broad, multiple dorsal or ventral branches of spinal

nerves can be seen to serially innervate each individual muscle. The innervations overlap within the muscle because of myotome overlap. In the case of limb muscles, each muscle is innervated by the branch of a single regional nerve. Because of multiple myotomes per muscle, the regional nerves must contain axons from ventral branches of multiple spinal nerves. The exchange of axons among ventral branches as they form regional nerves produces a nerve plexus for each limb.

Veterinary Pelvis and Perineum (Animal)

  Pelvis and Perineum

Pelvis  =  caudal region of trunk

                     The  pelvis consists of pelvic viscera within   pelvic                                         cavity that is bounded on five sides.

     

Pelvic Viscera:  

                                rectum & anal canal;  distal ureters, urinary  

                                bladder & urethra;

                                male or female genitalia;  blood vessels, 

                                lymphatics & nerves

 Pelvic Cavity Boundaries:

  cranial opening— pelvic inlet, bounded by sacrum, ilium &  

                                  pubis (rigid boundary)

   cavity walls— osseous pelvis + obturator & gluteal mm. &       

                            sacrotuberous ligament (dog)

     

   caudal boundary — perineum

Perineum  =    both a region & a wall

                                As topographic region:  from tail to scrotal  attachment or entire vulva; between ischiatic tuberosities.

As caudal wall of trunk: muscles,  fascia   &  skin  surrounding anal canal    and urogenital tract; includes

 1. Pelvic diaphragm = levator ani & coccygeus mm. associated

                                       deep fascia

2. Urogenital diaphragm = external urethral sphincter  associated    

                                               deep fascia                                                                                                                                                            3 External anal  sphincter m.

 4 Genital striated mm:

           

                 male    — bulbospongiosus m. & paired ischiocavernosus  

                                mm. 

                 female — constrictor vestibuli, constrictor vulvae &

                                  ischiocavernosus mm.

                                                 

 5. Smooth mm.: rectococcygeus  m.& retractor penis m.

  Micturition

Anatomy:

Urinary Bladder — apex; body; neck (trigone   = region of neck  demarcated by ureters & urethra).

Urethra — female: terminates in vestibule;

                      male: pelvic urethra  [preprostatic (cat); prostatic; &   

                       postprostatic regions] & penile urethra  

Musculature:

Detrusor m. = smooth muscle coat of apex & body; innervated by pelvic n  (S2 +S1 & S3 ) 

Internal urethral sphincter = smooth    m.; innervated hypogastric    n. (L2,  L3,  L4) 

               female   — vesical neck & cranial half of urethra 

               male      — neck (dog);  neck & preprostatic urethra (cat) 

External    urethral     sphincter   = urethralis m. (striated);       innervated  by pudendal n. (S2 & S3 + S1 ) 

               female — caudal half of urethra

               male — postprostatic urethra 

Urine Storage:

Sphincters  active via spinal  reflexes and detrusor    m. inhibited        

     - internal sphincter exerts tonic activity after bladder is half full 

     - external sphincter is activated voluntarily or reflexly during          phasic pressure increase

Micturition:

Requires prolonged detrusor contraction and sphincter inhibition 

    - free nerve endings (receptors) —>    GVA fibers in pelvic n.          —>   ascending          pathways —> pons —> descending spinal pathways —> activate detrusor & inhibit sphincters

Pain:

GVA pain   fibers travel through the hypogastric nerve to reach the spinal cord and brain.

veterinary Muscle & Body Biomechanics (Animal)

Muscle & Body Biomechanics

MUSCLE FIBER ARRANGEMENT

EFFECT ON STRENGTH

The amount of force that a muscle can generate is proportional to the cross-sectional area of muscle fibers (a.k.a. muscle cells) attaching to its tendon, i.e., the number of contractile proteins (actin and myosin) pulling on the tendon and contributing to

muscle force.

•  pennation design increases the number of muscle fibers (cross sectional area) attached to the tendon 

•  since force is a function of cross sectional area - a pennated muscle can generate more force than a comparable muscle with parallel fibers.

EFFECT ON SHORTENING

In this example, again consider two muscles - one with parallel fibers the other pennate

Assume each muscle fiber will contract to 50% of its resting length

Therefore:

•  with parallel-arranged muscle fibers the entire muscle can contract by 50% 

•  with the pennate arrangement each individual muscle fiber is pulling at an angle, resulting in reduced overall shortening of the entire muscle belly.

DEFINITIONS:

LINEAR FORCE:

Force can be broken down into various vectors. 

•  Vertical vectors (e.g. the downward forces due to body weight and the upward forces of the supporting surface)

•  Horizontal vectors (e.g. forces exerted to propel forward and

backward forces to brake forward motion)

With adequate force and friction (traction) the body can propel itself forward.  (practical application dictates a need for good traction to allow this forward motion – whoa to those leading a horse on ice)

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ROTATIONAL FORCE (TORQUE)  

 

Rotational force = force (F) x distance from fulcrum (d)

Limb rotation = muscle force (F) x distance from joint (d)

Torque input (muscle generated) = torque output (limb movement)

Muscles generate forces which when applied to the skeleton will generate rotation about a joint.   

MUSCLE ATTACHMENT EFFECTS 

The location of the muscle attachment (e.g. distance from joint) influences the resultant movement of that joint 

MECHANICAL ADVANTAGE VERSUS VELOCITY ADVANTAGE

Muscles that attach further from the joint have a mechanical advantage over muscles attached closer to the joint In the diagram below if muscles #1 and #2 were of equal strength (i.e., can generate the same force) then muscle #2 could produce a greater rotational force because its attachment is at a greater distance from the joint (rotational force = muscle force X distance from joint). 

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Conversely  muscles  that  attach  close  to  the point  of  rotation  are  able  to  produce  faster movement  of  the  lever  arm  than  muscle  that attach farther from the fulcrum.  In  the  diagram  to  the  right  if muscle  #1  and muscle  #2  both  contract  10% during  an identical time period  - muscle #1’s contraction would result  in a  larger movement of  the  lever arm  during  that  same  frame  of  time  than muscle  #2.    In  other  words,  muscle  #1  will result in a more rapid rotation - it has a velocity

advantage.

  

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Muscles attaching close to the joint with their velocity advantage are termed “high gear” muscles and those with a more distal attachment resulting in a mechanical advantage are termed “low gear” muscles.

It may be helpful to consider a similar gear analogy as in a car or bike.  At low gears the output force is relatively large  – allowing the vehicle to climb up a steep hill.  High gears on the other hand generates a lot of speed  – as would be advantageous in passing a vehicle. 

 

JOINT POSITIONING EFFECTS

THE BODY’S LEVER SYSTEM

Unique skeletal features result from functional adaptations over time.

In the figure below - the upper diagram is an example of an animal that uses it’s front limbs for digging; the muscles attached to the point of the elbow (olecranon) are positioned further from the elbow joint (fulcrum of movement) thereby generating large

forces for digging.  

The lower diagram with muscles attaching closer to the elbow joint is an runner adaptation that can result in a rapid rotation with muscle contraction

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For the same force and velocity input (left arrows), note the

relative magnitude of bolded arrows to the right of the diagrams –       a large downward force (F) is generated in upper diagram and

rapid rotation (V; velocity) of movement is produced in the

lower diagram.

veterinary Male Genitalia (Animal)

 Male Genitalia

Scrotum:    

situated between penis & anus

cutaneous pouch;  scrotal septum formed by dartos = “smooth  

cutaneous muscle” 

 spermatic  fascia: internal = a fibrous membrane (fibrous tunic) bound to parietal vaginal tunic 

         external = areolar connective tissue within dartos

         

 cremaster  muscle—   from internal abdominal oblique   m.; attaches to     internal spermatic fascia

 (not  developed  in the cat — where a levator scroti m. attaches to   the scrotal     septum )

 Testis:    pl.=  testes

         

produces spermatozoa and testosterone; coated by tunica albuginea (thick, white, c.t. capsule) & enveloped by visceral vaginal tunic 

  blood vessels are tortuous & highly branched for counter-current heat exchange;

  histologically, seminiferous tubules connect to a rete testis which connects to efferent ductules. which converge at the cranial pole of the testis to form epididymis.

Epididymis: 

spermatozoa storage & maturation occurs within the epididymis;  single coiled duct: head  —>  body  —>  tail  —>  ductus  deferens

proper ligament of the testis  —  homologous with proper ligament of ovary

ligament of the tail of epididymis —  (embryonic gubernaculum) homologous with round ligament of uterus

Ductus Deferens:   pl.= ducti deferentes

enveloped by visceral vaginal tunic connected to mesoductus deferens; traverses inguinal canal, penetrates prostate, & empties into urethra at the colliculus seminalis; terminal end of the ductus deferens features an ampulla (except in cat & pig) that has glands in its wall.

Spermatic  cord = ductus deferens + testicular vessels + vaginal tunics & spermatic fascia.

Accessory Genital Glands:  contribute seminal fluid to

                                                            the ejaculate  prostate (body + disseminated components) — all males. 

 bulbourethral glands (paired,  at ischial arch)  — not dog.

         

(vesicular glands [seminal vesicles] — neither dog nor cat )

 glands in wall of terminal segment of ductus deferens — all males

Penis:

three regions: root (contains bulb of penis & crus of penis),  body,  

                         and free part

 the penis is composed of: 1) penile urethra, 2) erectile tissue & 3)

                                              extrinsic muscles

Three bodies of erectile tissue:

corpus spongiosum penis: unpaired;  surrounds urethra;  begins as bulb of penis at root of penis

corpus cavernosum penis: paired; main erectile organ     (fibroelastic tunica albuginea)

crus of penis at the root of the penis — attaches to ischial arch;  covered by the ischiocavernosus m.;  replaced by os penis within free portion (carnivores)

glans (corpus spongiosum glandis)

dog : pars longa glandis & pars bulbus glandis (covers whole free portion)

cat : glans thin and distal [note: proximal skin has penil spines (cornified  papillae)]

Extrinsic penile muscles:    

bulbospongiosus m. (unpaired)— covers the bulb of the penis;

           

ischiocavernosus mm.(paired)—  covers the crus of the penis;

           

ischiourethralis mm. (paired)— small, inserts on ring around dorsal vein of penis;

retractor penis mm.(paired but together at midline) —smooth muscle;

 Prepuce:

cutaneous sheath which contains free part of penis (domestic mammals) 

 fascicles of cutaneous trunci m. encircling preputial orifice (dog)      = (retractor) preputial m.

Process of Erection: dog

parasympathetic effect — arterial vasodilation and venous constriction;

 

inflow to penis exceeds outflow and blood accumulates in penis;

pressure increases within fibroelastic capsules of erectile bodies;  

pressure mechanically compresses internal veins to further impede outflow;

contraction of extrinsic penile mm. pumps blood in against the increasing pressure; ischiourethralis m. occludes dorsal vein of penis to expand pressure within glans;

           

following intromission, the   superficially located dorsal veins   of penis, which drain

           

 the glans, are mechanically constricted. In the dog, the bulbus glandis expandsfollowing  intromission and this explains the  “tie” during copulation.

Ejaculation: 

          sympathetic pathway — contraction of ductus deferens, smooth m. in prostate & other glands, and internal urethral  sphincter (to prevent reflux   into bladder)

           also, contraction of urethralis m.& extrinsic penile mm.       

          propels ejaculate along urethra.

Veterinary IMMUNOLOGY (Animal)

IMMUNOLOGY

(Animal)

All living organisms are continuously exposed to substances that are capable of causing them harm. Most organisms protect themselves against such substances in more than one way with physical barriers, for example, or with chemicals that repel or kill invaders. Animals with backbones, called vertebrates, have these types of general protective mechanisms, but they also have a more advanced protective system called the immune system. The immune system is a complex network of organs containing cells that recognize foreign substances in the body and destroy them. It protects vertebrates against pathogens, or infectious agents, such as viruses, bacteria, fungi, and other parasites.

 Lymphocytes - Heart of the Immune System

Lymphocytes  - a class of white blood cells- are theprincipal active components of the adaptive immune system.

The other components are antigen-presenting cells, which trap antigens and bring them to the attention of lymphocytes so that thev can mount their attack.

When an antigen invades the body, normally only those lymphocytes with receptors that fit the contours of that particular antigen take part in the immune response. When they do, so-called daughter cells are generated that have receptors identical to those found on the original lymphocytes. The result is a family of lymphocytes, called a lymphocyte clone. with identical antigen-specific receptors. lymphocytes are made from stem cells in the bone marrow lymphocytes then undergo a second stage of development, or processing, in which they acquire their antigen-specific receptors.

 By chance, some lymphocytes are created with receptors that happen to be specific to normal, healthy components of the body. Fortunately, a healthy immune system purges itself of these lymphocytes, leaving only lymphocytes that ignore normal body components but react to foreign intruders. If this purging process is not completely successful, the result is an autoimmune disease in which the immune system attacks normal components of the body as though they were foreign antigens, destroying healthy molecules, cells, or tissues. Antibodies attack antigens by binding to them. Some antibodies attach themselves to invading microorganisms and render them immobile or prevent them from penetrating body cells. In other cases, the antibodies act together with a group of blood proteins, collectively called the complement system, that consists of at least 30 different components. In such cases, antibodies coat the antigen and make it subject to a chemical chain reaction with the complement proteins. The complement reaction either can cause the invader to burst or can attract scavenger cells that eat the invader.

Cytotoxic T cells destroy cells infected with viruses and other pathogens and may also destroy cancerous cells. Cytotoxic T cells are also called suppressor lymphocytes because they regulate immune responses by suppressing the function of helper cells so that the immune system is active only when necessary.

The receptors of T cells are different from those of B cells because they are trained to recognize fragments of antigens that have been combined with a set  of molecules found on the surfaces of all the body's cells. These molecules are called MHC molecules. As T cells circulate through the body, they scan the surfaces of body cells for the presence of foreign antigens that have been picked up by the MHC molecules. This function is sometimes called immune surveillance.

  

Immune Response

When an antigen enters the body, it may be partly neutralized by components of the innate immune system. It may be attacked by phagocytes or by preformed antibodies that act together with the complement system. Often, however, the lymphocytes of the adaptive immune system are brought into play. If lymphocytes encounter an antigen trapped by the antigen-presenting cells of the lymphoid organs, lymphocytes with receptors specific to that antigen stop their migration and settle to mount an immune response locally. As these

lymphocytes accumulate in the affected lymphoid tissue, the tissue often becomes enlarged for example, the lymph nodes in the groin become enlarged if there is an infection in the thigh area.

Antigen-presenting cells degrade antigens and ofteneliminate them without the help of lymphocytes. If there are too many antigens for them to handle alone, however, the antigen-presenting cells secrete IL- 1 and display fragments of the antigens to alert thehelper T cells. The IL-1 facilitates the responsiveness of T and B cells to antigens and, if released in large amounts, can also cause fever and drowsiness. Helper T cells that encounter IL-  1 and fragments of antigens transform into cells  called lymphoblasts, which then secrete a variety of interleukins that are essential to the success of the immune response. TheIL-2 produced by helper T cells promotes the growth of cytotoxic T cells, which may be necessary to destroy tumorous cells or cells infected with viruses. The IL-3 increases the production of blood cells in the bone marrow and thus helps to maintain  an adequate supply of the lymphocytes and lymphocyte products necessary to fight infections. Helper T cells also secrete interleukins that act on B cells, stimulating them to divide and to transform intoantibody-secreting plasma cells. The antibodies thenperform their part of the immune function.

The process of inducing an immune response is called immunization. It may be either natural through infection by a pathogen or artificial through the use of serums or vaccines. The heightened resistance acquired when the body responds to infection is called active immunity. Passive immunity results when the antibodies from an actively immunized individual are transferred to a second, nonimmune subject. Active immunization, whether natural or artificial, is longer-lasting than is passive immunization because it takes advantage of immunologic memory

Veterinary COMPLIMENT,OPSONISATION and PHAGOCYTOSIS (Animal)

COMPLIMENT,OPSONISATION                 

and 

PHAGOCYTOSIS

Opsonisation is the process of coating micro-organisms with plasma proteins to increase their adherence to phagocytic cells in preparation for phagocytosis. The two main opsonins are IgG antibody and the third component of complement

(C3) which bind to the surfaces of micro-organisms.

Phagocytic cells have membrane receptors for IgG (Fc piece) and activated C3 (which is called C3b). IgG antibody binds to micro-organisms because the Fab portion recognises bacterial epitopes. C3b binds because during activation of C3 a thiol bond is exposed which permits the formation of ester or amide bonds (covalent binding) with the bacterial surface structures. C3 is activated by limited proteolysis by enzymes called C3 convertases. There are two C3 convertases, one produced by activation of the classical pathway which is antibody dependent (IgM or IgG), while the alternative pathway can be activated in the absence of antibody. The classical pathway is inactivated when the C1q subcomponent of first component of complement binds to two adjacent IgG molecules or a single IgM molecule. The C1s subcomponent of C1 becomes an active protease and activates C4 and C2 to form the classical pathway C3 convertase which is a complex of activated C4 (C4b) and C2 (C2a) it is designated C4b2a. The alternative pathway is activated when micro-organisms come into contact with body fluids. The pathway is always being activated slowly to generate small amounts of activated C3 (C3b). When C3b binds to a micro-organism activation of the alternative pathway is amplified so that a large amount of the alternative pathway C3 convertase is

formed on the surface, followed by deposition of activated C3 (C3b). Complement can also kill micro-organisms directly. Once C3b has been formed, same binds to the C3 convertase to change it to a C5 convertase which activates C5 to form C5b. Subsequently C6, C7, C8 and C9 bind together with C5b to form a hollow cylinder which is inserted into cell membranes to produce lysis. Thus complement kills micro-organisms in two ways:

1. Opsonisation followed by phagocytosis and intracellular killing (indirect).

2. Assembly of the cytolytic C5b-9 membrane attack complex (direct).

Neutrophils and monocytes/macrophages are the two important phagocytic cells. Neutrophils and monocytes circulate in the blood and migrate into the tissues at the post-capillary venule. Initially they adhere to endothelium and then migrate through intercellular junctions. In the tissues they migrate  towards bacteria by means of a process called chemotaxis, which is defined as direct movement along a concentration gradients of chemotactic agents (e.g. C5a leukotriene B4, IL-8, bacterial peptides). Phagocytes recognise their targets by specific sugar residues (e.g. mannose or LPS) but binding is greatly enhanced if the organism is opsonised with IgG and/or C3b. Phagocytes possess Fc and C3b receptors and there is co-operation between these receptors. Thus an organism opsonised with IgG and C3b is more effectively phagocytosed. Ingestion (phagocytosis) is a localised endocytosis process requiring energy. The plasma membrane envelopes the particle and buds off to form an intracellular vesicle, the phagosome. Following fusion of the phagosome with lysosomal  granules the phagolysosome is formed and the bacteria are killed by oxygen-dependent and oxygen independent process.

Veterinary PHAGOCYTOSIS (Animal)

 PHAGOCYTOSIS

 Phagocytosis is a nonspecific defense mechanism in which

various phagocytes engulf and destroy the microorganisms

of disease.

Phagocytes.

Among the important phagocytes are the circulating white

blood cells called neutrophils and monocytes. In the tissues,

the monocytes are transformed into phagocytic cells called macrophages. The macrophages move through the tissues of the body performing phagocytosis and destroying parasites. They are part of the reticuloendothelial system. Phagocytes also initiate the processes of the immune system.

The process of phagocytosis begins with attachment and ingestion of microbial particles into a bubblelike organelle called a phagosome. Once inside the phagocyte, the phagosome containing the microorganism joins with a lysosome, which contributes enzymes. The fusion of phagosome and lysosome results in a phagolysosome. Microorganism    are destroyed within minutes, and the microbial debris is eliminated from the cell in the process of egestion. In the immune process, chemical portions of the microorganism called antigenic determinants are displayed on the surface of the phagocyte to stimulate the immune process.  

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Phagocytosis is enhanced by products of the immune system called antibodies.These protein molecules bind to microorganisms and encourage engulfing by phagocytosis.

The complement system. 

The complement system is a series of proteins that circulate

in the blood and encourage phagocytosis or otherwise complete the defensive process. Many immune reactions stimulate the complement system. The complement system operates in a cascade of reactions. In the pathway, certain complement components react with one another and produce new substances that induce other components to react. The results of the myriad reactions are substances that induce other complement components into action. The overall result is a number of substances toxic to microorganisms. The substances encourage phagocytosis or bring about destruction of microbial membranes.

Two general pathways for complement activity exist. The classical pathway  operates with the highly specific immune system and is initiated when certain antibodies unite with antigens and stimulate the complement system into action. The alternative  pathway is nonspecific and is initiated by tumors, cell wall components of bacteria, and various microorganisms. It is sometimes called the properdin pathway because properdin is one of the proteins

operating in it. The alternative pathway invokes a slower and less specific method for ridding the body of parasites, particularly Gram-negative bacteria and viruses.