The Nervous System

EFE Veterinary Science

Anatomy and Physiology

The Neuron: basic functional unit of the systemCell body

Axon

Dendrite

Image: ship.edu

Synapse: Where the action is!Neurotransmiters carry messages along a chain of neurons

ACTH, glutamate, GABA, norepinephrine, serotonin, others

Image: urbanchildinstitute.org

Myelin sheath provides insulation for greater speed

Axons covered with myelin sheaths appear white, forming the “white matter” of the brain and spinal cord. Cell bodies and dentrites appear grey, forming “grey matter”.

Image: epsych.msstate.edu

Basic Reflex Arc: Patellar tendon reflexStretch on patellar tendon->Afferent neuron->

spinal cord->efferent neuron->quadriceps muscle resulting in extension

Image: somemedicalthoughts.blogspot.com

Central v Peripheral nervous system

Image: NIM.NIH.org

Spinal CordWhite matter is myelinated

Grey matter contains nuclei

Spinal nerves exit to periphery

Image: Daviddarling.info

The hindbrain

Medulla--nuclei of cranial nerves

Pons—nuclei of cranial nerves

Cerebellum—center of balance and coordination

Kittens with cerebellar hypoplasia

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Midbrain

Also contains the nuclei of the cranial nerves

(more about them later!)

Forebrain

Made up of the diencephalon and the cerebral hemispheres

Diencephalon

Epithalamus = Pineal gland (remember endocrinology?)

Thalamus: The relay and integration center of the brain

Hypothalamus: Memory and endocrine regulation

Telencephalon = cerebrum = cerebral cortex

This is the grey wrinkly brain that we typically think of.

Animal brains also have an olfactory lobe!

Cortical lobes of the canine brain

Note the large olfactory lobe, which rests just caudal to the nasal conchae

Animals have a relatively smaller cerebral cortex

….as they do less abstract thinking and reasoning than humans.

Their more “primitive” brain areas are better developed.

The cerebral cortex (cerebrum)

Voluntary and conscious processing:• Voluntary movement is initiated

• Sensory input processed• Thought• Learning• Memory• Judegement• Language• personality

Special Pathways in the cerebral cortex

Several specialized pathways exist within the cerebral cortex:• Visual Pathway• Vestibular Pathway• Auditory Pathway• Somatic motor

pathways• Pyramidal• Extrapyramidal

• Visceral nervous system

Visual (and pupillary) pathway

Retina

Optic nerve

Optic chiasm (crossover)

Optic tract (over lateral thalamus)• Some to visual cortex• Some to neuronal

chains for direction of gaze, accomodation, pupil size

Vestibular Pathway

Vestibular fibers from the middle ear

Into brainstem

Some to vestibular nuclei

Some to cerebellum

Some to spinal cord

Some to nuclei for eye muscles

Conscious perception centered in the temporal lobe

Auditory Pathway

Cochlear nerve fibers

Cochlear nuclei in brainstem

On to 3 sites:• 2 for reflexes (such as

startle)• 1 to auditory cortex for

conscious perception of sound

Somatic Motor Pathways

Controls voluntary movement of the body

• Lower motor neurons • connect directly to

muscle fibers• control simple reflex

arcs

• Upper motor neurons • More complicated

reflexes• Initiate voluntary

movements

2 types of somatic motor pathways

Pyramidal• fine motor control

Extrapyramidal• Coarser movements

(gross motor)

Meanwhile, the autonomic nervous system

Essentiallly allows us to run on “autopilot” with our basic functions

Involuntary and generally outside of our awareness

Can be influenced by environment, emotion and drugs and medications

The Autonomic Nervous System

• Involuntary system• Controls internal

environment of the animal

• Senses changes and sends signals to:• Endocrine glands• Smooth muscle in

organs• Cardiac muscle

The Autonomic Nervous SystemTwo major branches:• Sympathetic

• Prepares for fight or flight response

• Increase heart rate• Dilate pupils• Bronchodilation

• Parasympathetic• Opposite to

sympathetic• Mainly vagus nerve• Slows heart rate• Constricts pupils

The Visceral Nervous System

Provides central (brain) control over maintenance of internal environment• Hypothalamus• Pituitary gland• Visceral afferents• Visceral efferents• Limbic system

Side note on the Limbic System

Most influenced by olfactory input

Also receives optic, auditory and touch from in and outside the body

Involved in emotional behavior: rage, fear, etc.

Also processing memories and “filing” them for later retrieval

Other structures associated with the nervous system

Meninges

Cerebrospinal fluid

Cranial nerves (12)

Spinal nerves

Peripheral nerves

Meninges

Tough fibrous membranes surrounding the brain and spinal cord

3 layers:

Dura matter

Subarachnoid

Pia matter

Meningitis

Epidural

Cerebrospinal fluid

Clear fluid

Surrounds the brain and spinal cord

Within the arachnoid space

Produced within the ventricles of the brain

The 12 Cranial Nerves

Responsible for sensory and motor function of head and face

Also major sensory functions

Each originates in a specific place in the brain

Don’t worry, you will get to memorize them later! (Lawhead page 150)

Spinal Nerves

Dorsal spinal nerve roots carry sensory information

Ventral roots carry motor function

In the spinal cord, the grey matter lies inside the white matter; in the brain, it is opposite.

Peripheral Nerves

Carry nerve impulses throughout the body

Brain -> spinal cord -> spinal nerve -> peripheral nerve for motor function

Peripheral nerve -> spinal nerve -> spinal cord -> brain for sensory

Usually combination of both.

(THE END)So, don’t be nervous! You’ll get this!