The nervous system

Question 1

Sensory

Answer 1

the nervous system senses changes from within the body or from outside of the body and conveys this information to the spinal cord and brain.

Question 2

Integrating

Answer 2

the sensory information received is analysed, stored and integrated to produce a response.

Question 3

Body

Answer 3

The integrated response may be to command muscles to move or produce glandular secretions

Question 4

Nervous tissue is classified as and functions as

Answer 4

Classified as:
neurons (aka nerve cells)
neuroglia (aka glia)
Functions:
neurons conduct nerve impulses,
while neuroglia protect and support neurons

Question 5

Neuroglia

Answer 5

Special connective tissue of nervous tissue.
Insulate neurons
Nourish neurons
Support neurons
Protect neurons

Question 6

Neuron’s

Answer 6

Monitor changes in the internal and external environment
Convert stimuli (which are detectable changes in the environment) to nerve impulses
Conduct these impulses to other neurons, muscle cells, or gland cells

Question 7

Cell body of a neuron

Answer 7

Cell body (Soma or perikaryon): includes nucleus and cytoplasm (containing normal cellular organelles).

Question 8

Dendrites of a neuron

Answer 8

Highly branched, short, numerous cell processes
Receive stimuli
From other neurons
May be modified as sensory receptors for heat, stretch, pressure
Bring impulses toward the cell body

Question 9

Axon in a neuron

Answer 9

Single process
Conducts impulses away from cell body to other cells (Nerve, muscle and gland cells).
A single axon may be called a nerve fiber
A single process can be very long i.e. a single axon in the horse may extend over two meters from the spinal cord all the way to the lower leg.

Question 10

Bundles of axons are called

Answer 10

Tracts in the CNS
Nerves outside the CNS

Question 11

Axons are covered in myelin called

Answer 11

Cell membrane of glial cells tightly wrapped around axon:
Schwann cells in the PNS
Oligodendrocytes in the CNS

Question 12

Myelin are

Answer 12

Myelin is an insulator that speeds the conduction of impulses along axons (faster than unmyelinated axons)
Myelin is white
Nervous tissue which contains lots of myelinated axons is called white matter
Nervous tissue which does not contain myelin looks dark, and is called gray matter
This type of nervous tissue often contains the cell bodies.

Question 13

CNS is

Answer 13

Central nervous system or CNS, is anatomically composed of the brain and the spinal cord.
Both are found in the center (cranial-caudal axis) of the animal’s body.

Question 14

PNS is

Answer 14

Peripheral nervous system or PNS
Those parts of the nervous system that extend away from the central axis toward the periphery of the body.
Composed of:
Cranial nerves which originate from the brain
Spinal nerves which emerge from the spinal cord.

Question 15

PNS system is divided into

Answer 15

The peripheral nervous system is subdivided into autonomic and somatic nervous systems based on their function

Question 16

Motor function

Answer 16

Voluntary control of skeletal muscles, such as conscious movement.

Question 17

Sensory function

Answer 17

Information that is consciously perceived
Information from the muscles, skin, eye or ear are consciously perceived information about the internal and external environment.
Many fibers are myelinated

Question 18

Autonomic nervous system: unconscious

Answer 18

Co-ordination of automatic (unconscious) body functions
Sensory and motor to the visceral structures (smooth and cardiac muscle and endocrine glands)
Automatically regulates a wide variety of functions e.g. heart rate and GI motility
Maintains internal balance or homeostasis
Many fibers are non-myelinated

Question 19

Sodium potassium pump

Answer 19

More sodium leaves than potassium enters
Net negative charge inside cell membrane
Membrane is polarized
Difference in charge across membrane is resting membrane potential
Nerve cells also have specialized sodium and potassium transport proteins
Can be called channels or gates
These are closed at rest

Question 20

Depolarization of neuron

Answer 20

Upon stimulation, Na+ channels open,
Allow only sodium to enter the cell
Moves down it’s concentration gradient by diffusion
Positive ions neutralize negative charge inside the cell
Called depolarization

Question 21

Repolarization of neuron

Answer 21

Na+ channel closes
K+ channels open
K+ ions flow out of cell
Outflow of K+ ions restores net negative charge inside of cell
Concentration gradient and electrical charges drive K+
The whole process of charge is rapid and is called an action potential

Question 22

Return to resting state of neurons

Answer 22

The difference between the repolarized and resting states is that the sodium ions are now on the inside of the membrane and potassium ions are on the outside of the membrane
Active transport by the sodium-potassium pump slowly restores ion concentrations

Question 23

Refractory period of neurons

Answer 23

During depolarization and early repolarization, the neuron cannot respond to another stimuli until it has re-established the resting membrane potential
Absolute refractory period
Will not respond under any circumstances
Relative refractory period:
During end of repolarization period
Possible to stimulate another depolarization if stimulus is ver large

Question 24

A nerve impulse

Answer 24

Electric charges cross cell membrane (depolarization), followed by repolarization.
Adjacent area is stimulated because opening of the gates is triggered by the change in voltage, spreading a wave of depolarization i.e. the nerve impulse is conducted along the nerve.
Cannot be conducted backwards because this area is refractory

Question 25

Threshold stimulus

Answer 25

Depolarization in response to a stimulus is strong enough to depolarize adjacent membrane and generate a nerve impulse All-or-Nothing principle If stimulus is too weak to open adjacent channels, the wave will not spread

Question 26

Saltatory conduction: rapid conduction in myelinated axons

Answer 26

Transmission of the impulse occurs from gap to gap Speeds the rate of conduction Called saltatory conduction Depolarization in myelinated axons can only take place at the gaps called the nodes of ranvier

Question 27

How neurons communicate

Answer 27

Transmission of impulses from one neuron to the next cannot occur directly because they don’t touch Synapse is the junction between two neurons or between a neuron and a target cell The gap is called the synaptic cleft Many neurons will have more than one synapse, and many will have thousands Allows complex integration of signals The presynaptic neuron releases a neurotransmitter Received by the postsynaptic neuron

Question 28

Synaptic end bulb is

Answer 28

The synaptic end bulb is the end of the presynaptic axon Contains many mitochondria Provide energy Has neurotransmitters in vesicles Releases the neurotransmitters when a wave of depolarization reaches the end bulb and opens calcium channels Neurotransmitters diffuse across the synaptic cleft to bind to receptors specific for that neurotransmitter on the postsynaptic membrane of the other cell Membrane depolarizes

Question 29

Types of neurotransmitters and their effect on postsynaptic membrane

Answer 29

Postsynaptic membranes may have receptors for more than one neurotransmitter There are excitatory and inhibitory types of neurotransmitters (NT) Excitatory NT will tend to cause depolarization Inhibitory NT will tend to increase the polarization (hyperpolarize) of the membrane and make it less likely to depolarize/fire (i.e. Will help prevent a signal from being transmitted) The relative balance of excitatory NT and inhibitory NT determines the overall effect on the postsynaptic membrane – called summation

Question 30

Acetylcholine

Answer 30

Very common NT in the body Can be excitatory or inhibitory, depending on where found Excitatory at somatic neuromuscular junctions Inhibitory on the heart (slows rate)

Question 31

Norepinephrine, dopamine, and epinephrine

Answer 31

Group of NT called catecholamines Norepinephrine – associated with ‘fight or flight’ Epinephrine – also ‘fight or flight’, but can be released from the adrenal medulla as a hormone as well as a NT Dopamine – found in the brain and is important for autonomic functions, muscular control, and muscular control

Question 32

Gamma-aminobutyric acid (GABA) and glycine

Answer 32

Inhibitory NT GABA is in brain Glycine in spinal cord Some tranquillizers affect GABA receptors to increase its inhibitory activity in the brain → sedation Diazepam (valium)

Question 33

Drugs and neurotransmitters

Answer 33

Drugs or toxins mimic neurotransmitters by activating the same receptors Opiates: bind receptors normally used by endorphins to provide analgesia and euphoria Diazepam and alcohol affects GABA receptors, therefore inhibitory Strychnine - A toxin that inactivates inhibitory receptors resulting in excitatory effect Dogs may are dentally or purposely be poisoned Mostly banned in Canada

Question 34

Stopping and recycling the neurotransmitter

Answer 34

Normally, enzymes break down the NT to remove it from the receptor to end the stimulus Often the breakdown products are reabsorbed by the synaptic end bulb and recycled

Question 35

4 sections of the brain

Answer 35

Cerebrum Cerebellum Diencephalon Brainstem

Question 36

Cerebrum is and does what

Answer 36

Largest part of the brain in domestic animals Responsible for functions of "higher order" behaviour such as learning, intelligence, awareness. Conscious awareness and movement Divided into 2 hemisphere or halves by a median fissure or groove Each half is connected to the contralateral, or opposite side of the body via the corpus callosum

Question 37

Outer part of cerebrum

Answer 37

Gray matter of cerebral cortex Contains neuron cell bodies

Question 38

Inner part of cerebrum

Answer 38

Inner part is white matter Contains axons sheathed in myelin

Question 39

The surface of the cerebrum

Answer 39

The surface is wrinkled due to the folds called gyri Separated by deep grooves called fissures and shallow grooves called sulci

Question 40

Cerebellum is and does

Answer 40

Second largest part of brain Allows coordinated movement, balance, posture, and complex reflexes Compares the intended movement with the actual position of muscles and joints (proprioception) Determines if the intentions of the cerebral cortex are being carried out If not, the cerebellum stimulates or inhibits the muscles to fine-tune the movement Uses same feedback system to maintain posture and balance Damage or disease of the cerebellum results in hypermetria Voluntary movements become jerky and exaggerated May see abnormal gait

Question 41

Diencephalon

Answer 41

Pathway between the brainstem and the cerebrum

Question 42

thalamus of diencephalon

Answer 42

central relay centre for sensation and motor impulses Interprets sensation and sense it to cerebrum Emotions, language memory

Question 43

Hypothalamus and pituitary

Answer 43

Coordinates the endocrine system and homeostasis by managing autonomic functions (i.e. GI motility, temperature,etc.)

Question 44

Brainstem is

Answer 44

Connection between the brain and the spinal cord Composed of the midbrain, pons and medulla oblongata Responsible for maintenance of basic support functions of the body Operates at subconscious level

Question 45

Three vital reflexes of the brainstem

Answer 45

Cardiac centre - rate and strength of heart contractions Vasomotor centre - regulation of diameter of blood vessels (hence blood pressure) Respiratory centre - regulation of rhythm of breathing Non-vital reflex centres include - cough, sneeze, swallowing, and vomiting

Question 46

Meninges

Answer 46

Connective tissue membranes that surround the brain and spinal cord Carry a complex network of blood vessels Supply nutrients and oxygen to the superficial tissues of the brain and spinal cord Fluid, fat and connective tissue found between the layers Cushions the brain Inflammation of the meningeal membranes from virus or bacterial infections is called meningitis In the distal spinal cord, the dura separates from the vertebrae. Epidurals are given into the space just outside the dura

Question 47

Dura mater

Answer 47

tough outer membrane next to the bone of the cranium Separated from arachnoid by the narrow subdural space

Question 48

Arachnoid

Answer 48

second layer Forms trabeculae, a web-like structure Cavities in the web are called the subarachnoid space This is where CSF is foun

Question 49

Pia mater

Answer 49

innermost membrane Follows surface of the CNS and is only separated from nervous tissue by a thin layer of neuroglial processes

Question 50

Cerebrospinal fluid is and circulates through

Answer 50

Fluid that bathes and protects the brain and spinal cord Formed by filtration and secretion from capillary networks called the choroids plexus, located in the ventricles of the brain Circulates through: Cavities (canals and ventricles) inside the brain and spinal cord Then through pores into the subarachnoid space

Question 51

Blood brain barrier is

Answer 51

A functional barrier separating the capillaries in the brain from the nervous tissue itself The capillary walls are relatively impermeable (unlike in the rest of the body) Capillary wall cells in the brain are aligned tightly together without openings Are covered by the cell membranes of glial The barrier prevents many drugs, proteins, ions and other molecules from readily passing from the blood into the brain

Question 52

Blood brain barrier protects how

Answer 52

Protects the brain from many poisons circulating in the bloodstream Kills insects by affecting their nervous system - they do not have a blood brain barrier Collies have genetic mutation making them more susceptible to toxicity from anti-parasitics Makes treatment of infections such as meningitis or meningoencephalitis difficult Many antibiotics and anti-inflammatories cannot penetrate into the brain and meninges

Question 53

Cranial nerves

Answer 53

Special set of 12 pairs of nerves in PNS Originate from brain Mainly responsible for motor and sensery innervations of structures of the head Includes Vision, hearing, voice, taste and smell Tongue, head & facial sensation and expressions May be sensory, motor, or both

Question 54

Spinal cord

Answer 54

Generally, decreases in size from cranial to caudal. Areas of enlargement at the caudal cervical and mid lumbar regions Composed of inner grey matter (nerve cell bodies) surrounded by white matter (nerve cell processes). Note that the arrangement is opposite to the brain.

Question 55

Spinal nerves are

Answer 55

Spinal nerves emerge from the spinal cord Pairs emerge through intervertebral foramen between adjacent vertebrae of the spine Spinal nerves come off the spinal cord as dorsal and ventral roots which join up to travel to the affected structure

Question 56

Spinal nerves are named and numbered by

Answer 56

Dorsal root - carries sensory info from body to spinal cord Ventral root - carries motor info from spinal cord to body They are named and numbered the same as the vertebrae they are adjacent to in the thoracic, lumbar and sacrum (except at C1 and coccygeal vertebrae)

Question 57

Spinal nerves emerge from and plexuses

Answer 57

Spinal nerves that emerge from the spinal cord go to somatic structures The spinal nerves that go to appendages initially form braid-like arrangements known as plexuses The brachial plexus – innervates the thoracic limb from last 3-4 C and first 1-2 T spinal nerves The lumbosacral plexus –from last 3-5 L and first 1-3 S spinal nerves, innervates the pelvic limb.

Question 58

Structure of the SNS

Answer 58

Sympathetic nerves come off the spinal cord in the thoracic and lumbar areas Called the thoracolumbar system

Question 59

Structure of the PNS

Answer 59

Parasympathetic nerves come off the brain and the sacral area of the spinal cord Called the craniosacral system

Question 60

The motor nerves of PNS and SNS

Answer 60

The motor nerves of both have 2 neurons in sequence First neuron body is in the brain or spinal cord The axon extends out from the CNS to a cluster of neuronal cell bodies called a ganglion The preganglionic neuron. Second neuron synapse with the second neuron at the ganglion Connects to the target organ Postganglionic neuron

Question 61

SNS basic functions

Answer 61

Bronchodilation- to increase air intake Increased heart rate and contractility- to maximize circulation to muscles Vasodilation to muscles Vasoconstriction to skin, GI, kidney- redirecting blood to critical organs Pupil dilation (increases peripheral vision)

Question 62

PNS general functions

Answer 62

Decreases bronchodilation Decreases HR and contractility Decreases vascular changes caused by sympathetic system Increases GI activity- digest Pupil constriction

Question 63

Acetylcholine is

Answer 63

the neurotransmitter for all the preganglionic synapse, and post ganglionic parasympathetic Cholinergic receptors- 2 types

Question 64

Norepinephrine is

Answer 64

the neurotransmitter for all post- ganglionic synapse of the sympathetic system only AKA: epinephrine/adrenalin Adrenergic receptors- 3 types All preganglionic nerve fibers use acetyl choline as the neurotransmitter

Question 65

Nerotransmitters in the pNS

Answer 65

Uses acetylcholine as a NT at both pre and post synaptic neurons Therefore acetylcholine – releasing neurons are called cholinergic neurons

Question 66

Nicotinic receptors

Answer 66

on the postganglionic neurons of Parasympathetic NS Sympathetic NS Voluntary muscle motor neurons Nicotine is a nicotine receptor agonist- is a stimulant

Question 67

Muscarinic neurotransmitters

Answer 67

primarily target organs of parasympathetic NS Stimulation increases salivation, increased GI motility, decreased heart rate, constricts pupil ANtagonist- atropine blocks this receptor, reverses parasympathetic signs increases HR, produces salivation, GI motility

Question 68

Adrenergic receptors 3 types are and are located in

Answer 68

Alpha1: in blood vessels cause vasoconstriction in skin, GIT, and kidneys with sympathetic stimulation Beta1: in heart Cause increase HR and contractility Beta2: in bronchi Cause bronchodilation

Question 69

Somatic reflexes

Answer 69

Somatic: skeletal muscle contraction (blinking, ducking, sneezing, withdrawal from painful stimuli)

Question 70

Autonomic reflexes

Answer 70

smooth muscle, cardiac, and endocrine glands (control of HR, pupil size, GI motility)

Question 71

Reflex arc is

Answer 71

→sends signal along sensory neuron to gray matter of spinal cord or brainstem →synapses with interneurons →integrate information with other sensory neurons →reflex response sent out by motor neuron → effect caused at skeletal muscle, smooth muscle, cardiac, or endocrine gland (i.e. The effector organ) →No conscious control is necessary!!!!!

Question 72

Stretch reflexes

Answer 72

Example is the patellar reflex Simple reflex Sensory information from stretch (muscle spindle) in quadriceps muscle Senses stretch and sends information up a sensory neuron to the spinal cord At the spinal cord, synapses with the efferent motor neuron that innervates the same muscle Causes a contraction Another branch of the sensory neuron synapses at the spinal cord with an inhibitory motor neuron of the opposing muscle – causing it to relax

Question 73

Withdrawal reflex

Answer 73

Flexor reflex – example is rapid withdrawal of hand from hot stove Strong stimulus (usually painful) causes rapid withdrawal of limb Reflex arc stimulates withdrawal muscles and inhibits the opposing muscles to allow rapid, complete withdrawal Limb is withdrawn before the brain receives, and consciously perceives, the message of pain Toe pinch- only the leg tested should withdraw Crossed- extensor reflex- normal for the opposite leg to extend

Question 74

Role of upper CNS in moderating reflexes

Answer 74

Since spinal reflexes don't require input from the brain, damage to the spinal cord at L1 or L2 can still allow reflexes to occur in the hind leg Would be controlled by the spinal cord in L3 or lower Brain would not receive the sensory information through the damaged area The difference if there is damage to L1 or L2, is that the reflexes will be increased in intensity – become exaggerated Hyperreflexia occurs because normally the upper CNS would have an inhibitory effect to modify the reflex Modification can’t occur with spinal cord trauma Hyporeflexia can occur if the trauma occurs anywhere in the actual reflex arc, including the part of the spinal cord involved in the reflex Can use changes in intensity of reflexes to help localize lesions

Question 75

Babinski reflex

Answer 75

Scrape the pointy tip of the hammer up the metacarpus or metatarsus. If the upper SC is damaged, then may see extension of the digits – this is abnormal.

Question 76

Menace

Answer 76

Move fingers towards patient’s eye Patient blinks CN II and VII May not be present in neonates Develops around 12 weeks old

Question 77

PLR

Answer 77

Pupillary light reflex (PLR): requires retina, optic nerve (CNII), neuron clusters in the diencephalons, motor neurons of CN III (supply the iris muscles) Must have direct and consensual response to be normal Does not mean animal can see –damage to the cerebral cortex causes blindness with normal PLR Should not be present during surgical anesthesia

Question 78

Palpebral reflex

Answer 78

When the medial canthus of the eye is touched, the eye closes Requires trigeminal and facial nerves Sensation to face, motor to face Used to monitor the depth of anesthesia. If the palpebral is present, the patient can still feel the surgery.

Question 79

Corneal reflex

Answer 79

Contact to cornea causes a blink and retraction of eye in the orbit Requires receptors in the corneal epithelium, sensory neurons in CN V, brainstem, and motor neurons in CN VII to cause blink Reflex diminishes with depth of anesthesia But danger with corneal damage Often used to help pronounce death after euthanasia

Question 80

Regeneration and repair in the nervous system

Answer 80

In general, neurons are incapable of mitosis, therefore the body can’t replace nerve cells lost to injury or disease Axons can regenerate as long as disease is mild and cell body is intact Regenerate 2-4mm/day Severe injuries can take months or not at all

Question 81

Righting position

Answer 81

Set in lateral recumbency- animal should right itself Held upside down by hips- animal should hold its head up