The Anatomy of the Nervous System

Question 1

What are the key components of the typical neurone?

Answer 1

1. Dendrites. These receive electrical stimuli. They help to facilitate movement towards the presynaptic terminal.
2. Axon. This is responsible for moving the action potential. Improved movement is achieved using schwann cells.
3. Cell body. Contains the nucleus and the organelles.
4. Schwann cells. These keep peripheral nerve fibres alive.
5. Nodes of ranvier. These allow action potential to jump, so it speeds up its movement.

Question 2

What type of neurone are there?

Answer 2

1. Unipolar - projection divides into a single axon.
2. Bipolar - one axon and one dendrite. Very rare and only found in the retina and in the inner ear.
3. Multipolar - one axon and several dendrites. Found in the brain and in the spinal cord.
   Within a nerve cell, many nerve fibres group together to form a nerve.

Question 3

Describe the brain

Answer 3

A horse’s brain is approximately 650g (about one % of its totoal body weight). The brain and the spinal cord have similar structure, but reversed:
The brain has grey matter on the outside and white matter on the inside whereas the spinal cord has white matter on the outside and grey matter on the inside.

Question 4

What are the two nervous systems?

Answer 4

The central and peripheral nervous systems.

Question 5

What are the regions of the brain?

Answer 5

Telecephalon, diencephalon, mesencephalon, merencephalon and myencephalon

Question 6

Describe the forebrain

Answer 6

The largest part of the brain.
There are two central hemispheres that are divided and connected by white matter. The connection is made by axon and nerve cells.
Each hemisphere has 4 lobes - frontal, parietal, occipital and temporal. The surface is made up of highly folded tissue which makes up most of the space.
Has an important role in memory, emotions, will and behaviour.
Each lobe is mirrored on both sides of the brain.

Question 7

Describe the midbrain

Answer 7

This is sensory orientated. It focuses on auditory and visual reflexes.

Question 8

Define the TECTUM

Answer 8

The tectum is the section of the midbrain that focuses on auditory and visual reflexes. It is the ‘ceiling’ of the midbrain.

Question 9

Define the TEGMENTUM

Answer 9

The tegmentum is the ‘floor’ of the midbrain. Along with the tectum, it passes information gained from the external environment to the cerebrum in the forebrain.

Question 10

Describe the hindbrain

Answer 10

There are 3 regions within the hindbrain:

1. Pons - acts as a bridge that connects the left and right hemispheres, along with the corpus callosum
2. Cerebellum - responsible for balance and muscle coordination. Also has strong links to behaviour.
3. Medulla oblongata - controls all brain impulses for life. It is important for movement, circulation, the digestive system, and the endocrine system to link to the brain.

Question 11

What are the cranial nerves?

Answer 11

Olfactory (nose/mouth), optic (eye), ocolomotor (eye movement), trochlear (ear), trigminal (facial), abducens (vision, facial, vestibulocochlear (ear), glossopharyngeal (voicebox), vagus (heart/lungs), spinal accessory, hypoglossal (tongue).

Question 12

Describe the spinal cord

Answer 12

Runs down the centre of the vertebrae from the medulla oblongata to the 2nd lumbar vertebrae. Spinal nerves branch from the spinal cord. They receive afferent impulses and send efferent impulses. There are 42 pairs of spinal nerves.
Spinal nerves carry messages to and from the different areas of the spinal cord.

Question 13

What is the relationship between the PNS and the CNS?

Answer 13

The central nervous system covers everything: the peripheral is a part of it.
The CNS alone controls the afferent division and somatic and visceral pathways.
The PNS controls the efferent (motor) division as well as the autonomic (sympathetic and parasympathetic NS) and the somatic NS.

Question 14

Describe the process of touch/pain conduction

Answer 14

Free nerve endings connect with small diameter fibres to convey pain and large diameter fibres to convey touch. Pain and temp changes are detected by the PNS but each take a slightly different route.

Question 15

What is the autonomic nervous system?

Answer 15

It involves the involutary innervation of smooth and cardiac muscle and glands. It has two divisions: the parasympathetic and the sympathetic.
The sympathetic system turns stuff on - relates to energy generation e.g. fight or flight response.
The parasympathetic system turns stuff off - promotes a calming response from organs with the aim of returning to self-maintenance functions.

Question 16

What are the 5 senses?

Answer 16

Sight, smell, touch, taste, hearing

Question 17

What are the main parts of the eye?

Answer 17

The sclera (tough outer layer), cornea (transparent, lets light into the eye), pupil (the hole through which light passes), iris (controls the size of the pupil).

Question 18

What happens when there is dim light projected onto the eye?

Answer 18

The pupil (controlled by the muscles in the iris) expands to let a lot of light in, in order to improve visibility.

Question 19

What happens when there is bright light projected onto the eye?

Answer 19

The pupil (controlled by the muscles in the iris) contracts and lets only a little light in. This protects the delicate stem and rod cells in the retina.

Question 20

Define the RETINA

Answer 20

The retina is a light sensitive layer that contains two types of sensory receptor cells: cone and rod cells.

Question 21

What are the parts of the horse’s ear?

Answer 21

1. The pinna (external ear) - 16 muscles allow 180 degree movement. Used as a means of communication but horses can also hear up to 25,000 Hz.
2. The middle ear - soundwaves bounce off the tympanic membrane (eardrum) and g along 3 auditory occicles (malleus, incus, stapes).
3. The inner ear - contains the cochlea and semi-cochlea canals. Vibrations on the oval window, then sound waves are converted into nerve impulse which are sent to the brain.

Question 22

Describe the horse’s sense of taste/smell

Answer 22

This is a well developed sense in the horse as it is needed for safety and plays a large role in behaviour (flehmen response). Air moving over the turbinate bones send messages to the brain via the olfactory sensory fibres in the nasal cavity.

Question 23

Describe the horse’s sense of touch

Answer 23

Linked closely to smell and is well developed in the horse (the muzzle is the most sensitive area of the body) Skin is sensitive to pressure and temperature. It is important for social behaviour but too much stimulation can result in numbness.

Question 24

What is the cauda equina?

Answer 24

The cauda equina is a collection of spinal nerves that send individual nerves off. These nerve fibres feed down into the limbs.