Anatomy Session 2 - Neuro

Question 1

Define Cranial

Answer 1

Towards the head

Question 2

Define Caudal

Answer 2

Towards the back (tail end)

Question 3

Define Rostral

Answer 3

Towards the face

Question 4

What does the CNS consist of?

Answer 4

Brain and spinal cord

Question 5

What does the PNS consist of?

Answer 5

all nervous tissue outside the CNS, primarily nerves:
● cranial nerves (arise from the brain)
● spinal nerves (arise from the spinal cord)
● autonomic nerves

Question 6

What does the somatic NS do?

Answer 6

controls voluntary activities; under conscious control.

Question 7

What does the autonomic NS do?

Answer 7

controls involuntary activities; not under conscious control.

Question 8

What is the brain divided into?

Answer 8

the cerebrum
the cerebellum
the brainstem

Question 9

What is the cerebrum?

Answer 9

-largest part of the brain
- composed of masses of neurons and supporting cells

● composed of left and right cerebral hemispheres, connected to each other.
● The surface = cerebral cortex. It contains neuron cell bodies = grey matter. Information is processed in the grey matter.
● The cerebral cortex is folded. The folds are called gyri (singular: gyrus), and the grooves between the folds are called sulci (singular: sulcus).

Question 10

What is deep to the cerebral cortex, within the cerebral hemispheres?

Answer 10

● masses of axons = white matter. Information is transmitted through bundles of fibres in the white matter.

● collections of cell bodies called nuclei - grey (nucleus = a collection of cell bodies within the CNS).

Question 11

What are the four lobes of the cerebral hemispheres?

Answer 11

Frontal, parietal, occipital and temporal lobes

Question 12

What is the cerebellum?

Answer 12

Means ‘little brain’
- cerebellum lies inferior to the posterior part of the cerebrum.

Like the cerebrum, the cerebellum:
- composed of left and right hemispheres that are connected to each other
- has a highly folded cortex
- contains white matter and nuclei deep to the cortex

Question 13

Where is the cerebellum?

Answer 13

The cerebellum is attached to the brainstem. The cerebellum functions in balance, coordination, and movement, but operates beyond our conscious control.

Question 14

What is the brainstem composed of?

Answer 14

• midbrain
• pons
• medulla

Question 15

Where is the brainstem and what does it do?

Answer 15

It lies inferior to the cerebrum and anterior to the cerebellum (and is attached to both). It:

• relays information between the cerebrum, spinal cord and cerebellum
• gives rise to most of the cranial nerves
• contains ‘centres’ that regulate breathing and consciousness.

Question 16

Where is the spinal cord?

Answer 16

The spinal cord is continuous with the medulla of the brainstem and is protected by the vertebral column. The spinal cord is shorter than the vertebral column; the cord ends around the level of the first and second lumbar vertebrae (L1 - L2).

Question 17

What does the spinal cord contain?

Answer 17

Contains neurone cell bodies = grey matter. The grey matter is surrounded by white matter that connect different parts of the CNS to each other.

Thirty-one pairs of spinal nerves - they carry information between the spinal cord (CNS) and periphery (e.g. skin, muscles).

Question 18

What does the brain contain?

Answer 18

Cavities inside called ventricles which are continuous with each other and filled with Cerebrospinal Fluid (CSF).

Question 19

What is CSF made from and does?

Answer 19

Produced by specialised cells within ventricles. It then leaves ventricles through small openings and surrounds the brain and spinal cord.

It:
- provides nutrients to the brain
- protects the brain by providing a cushion against trauma
- prevents delicate nerves and vessels from being compressed between the brain and the internal surface of the skull.

(4 ventricles)

Question 20

What are meninges?

Answer 20

Membranes that lie between the brain and spinal cord - three meningeal layers - dura mater, arachnoid mater, and pia mater

Question 21

Where are the layers?

Answer 21

1st layer = dura mater - It is thick and strong. dural folds project into the cranial cavity.
2nd layer = arachnoid mater - is thin and loosely encloses the brain and spinal cord.
3rd layer = pia mater - It adheres to the surface of the brain and spinal cord. It is very thin and cannot be seen with the naked eye.

Question 22

What supplies the brain?

Answer 22

the left and right internal carotid arteries and the left and right vertebral arteries.

Question 23

What gives rise to the circle of Willis?

Answer 23

On the inferior surface of the cerebrum, the internal carotid and vertebral arteries give rise to branches that form an interconnected ring called the Circle of Willis.

Question 24

What does the circle of Willis give rise to?

Answer 24

The Circle of Willis gives rise to three cerebral arteries on each side (which supply the cerebral hemispheres), cerebellar arteries (which supply the cerebellum), and arteries that supply the brainstem and spinal cord. Communicating arteries connect the cerebral arteries with each other.

Question 25

What is a stroke?

Answer 25

Blockage of an artery leading to death of brain tissue

Question 26

What drains the brain?

Answer 26

Veins drain blood from the brain. Both superficial and deep. There are also large veins enclosed within the dura mater called dural venous sinuses.

Question 27

What is the somatic NS composed of?

Answer 27

The somatic nervous system controls voluntary activities. It has a motor and sensory component.

● The motor component controls the voluntary contraction of skeletal muscle. For example, it controls the movement of our limbs, trunk, and face.

● The sensory component carries information about peripheral stimuli from the sensory receptors in the body to the CNS, which reaches our conscious perception (e.g. touch, pain, temperature).

Question 28

What does the autonomic NS give rise to?

Answer 28

The autonomic nervous system (ANS) controls involuntary activities such as heart rate, blood pressure, respiration, digestion, and sexual arousal. Like the somatic system, the ANS has a motor and sensory component.

● The motor component of the ANS controls smooth muscle, glands, and cardiac muscle. It is subdivided into two parts:
● the sympathetic nervous system = ‘flight and fight’
● the parasympathetic nervous system = ‘rest and digest’.

● The sensory component of the ANS conveys sensory information about the internal environment from the viscera (organs) to the CNS, but it does not reach our conscious perception. An example is blood pressure monitoring

Question 29

What are visceral afferent nerves?

Answer 29

Sympathetic and parasympathetic nerves. They are also called visceral efferent nerves, as they leave the CNS. They have generally opposite but coordinated actions.

Question 30

What occurs in the sympathetic system?

Answer 30

The sympathetic system prepares the body for the four F’s: ‘fight, flight, fright and freeze’:
● heart rate increases and the bronchi dilate. Peripheral blood vessels constrict and divert blood away from the skin and gut to the skeletal muscles in preparation for activity. The pupils dilate, hair stands on end and sweat glands are stimulated.

Question 31

What occurs in the parasympathetic system?

Answer 31

The parasympathetic system prepares the body for ‘rest and digest’:
● heart rate decreases and the bronchi constrict. Glands are stimulated (e.g. salivary glands, digestive secretions) and gut activity (peristalsis) is stimulated. The pupils constrict.

The sympathetic and parasympathetic systems share the same basic anatomical arrangement, but with some important differences. In both systems, there are two neurons in the pathway from the CNS to the target organ (effector).

Question 32

Where do the cell bodies of neurons lie in the CNS?

Answer 32

The cell bodies of the first neurons lie in the CNS:

● sympathetic neuron cell bodies lie in the thoracic and upper lumbar segments of the spinal cord (T1 - L2/3).
● parasympathetic neuron cell bodies lie in the brainstem and sacral spinal cord (S2 - S4).

● Their axons leave the CNS and synapse with a second neuron, whose cell body lies in a ganglion (a collection of cell bodies outside the CNS).

● For this reason, the first neuron is called a preganglionic or presynaptic neuron, and the second neuron is called a postganglionic or postsynaptic neuron.

● The postganglionic fibres travel to target organs.

Question 33

What is the differences in where the sympathetic and parasympathetic ganglia lie?

Answer 33

Sympathetic ganglia lie closer to the CNS than to target organs, so their preganglionic axons are short, and their postganglionic axons are long.

Parasympathetic ganglia lie very close to target organs (or even within them) so their preganglionic axons are long, and their postganglionic axons are short.

Although both systems innervate the thoracic, abdominal, and pelvic viscera, the sympathetic system is far more widely distributed than the parasympathetic system. Because sympathetic nerves innervate sweat glands and smooth muscle in the blood vessel walls and hair follicles (the arrector pili muscles), they reach every part of the body.

Question 34

What is the sensory component of the ANS?

Answer 34

Sensory Component of the ANS

The sensory component of the autonomic nervous system carries sensory information from the viscera to the CNS, but it does not usually reach our conscious perception. Sensory autonomic fibres are also called visceral afferent fibres, as they bring information back to the CNS. Visceral afferents travel back to the CNS along the paths of the sympathetic and parasympathetic nerves.

● Sensory autonomic fibres send information about our internal environment back to the CNS (e.g. blood pressure, levels of oxygen and carbon dioxide in our blood). These sensory inputs elicit reflex (automatic, unconscious) responses, which constantly maintain our internal environment.
● These fibres also convey information to the CNS about distension, stretch, spasm or ischaemia of the viscera, which may cause pain or discomfort that does reach consciousness.

● The distribution and course of visceral afferents is clinically important and relevant to the phenomenon of referred pain. We will learn more about referred pain later in the course.

Question 35

Where do cranial nerves arise from?

Answer 35

Cranial nerves arise from the cerebrum and brainstem. There are twelve pairs which are numbered I - XII.

Question 36

Where do cranial nerves exit?

Answer 36

Through holes in the base of the skull called foramina (singular = foramen)

Question 37

What type of fibres do cranial nerves carry?

Answer 37

All fibre types e.g. sensory, motor + special senses and a mix except sympathetic fibres

Question 38

What are the spinal nerves?

Answer 38

Thirty-one pairs of spinal nerves are attached to the spinal cord. A pair of spinal nerves corresponds to each segment of the spinal cord. We have:

• 8 pairs of cervical spinal nerves (C1 - C8)
• 12 pairs of thoracic spinal nerves (T1 - T12)
• 5 pairs of lumbar spinal nerves (L1- L5)
• 5 pairs of sacral spinal nerves (S1 - S5)
• 1 pair of coccygeal spinal nerves (Co1).

Question 39

What fibres do spinal nerves carry?

Answer 39

The spinal nerves are mixed nerves and carry:
* somatic motor fibres from the CNS to the body
* somatic sensory fibres from the body to the CNS
* sympathetic (i.e. autonomic motor) fibres from the CNS to the body.

Question 40

Where do spinal nerves pass through?

Answer 40

The vertebral column protects the spinal cord. Spinal nerves pass through the gaps formed between adjacent vertebrae, the intervertebral foramina.

Question 41

Where do somatic motor fibres lie?

Answer 41

The cell bodies of the motor neurons lie in the ventral horn of the spinal cord. The axons leave the cord via a series of rootlets, which merge to form the ventral (motor) root of the spinal nerve. These motor fibres stimulate the voluntary contraction of skeletal muscle.

Question 42

Where do somatic sensory fibres lie?

Answer 42

The cell bodies of peripheral sensory neurons lie in the dorsal root ganglia (DRG) which are visible with the naked eye as small ‘swellings’ on the dorsal roots. Instead of a single axon, these neurons have two processes, one that projects peripherally into the spinal nerve and one that projects centrally into the dorsal horn of the spinal cord.

Sensory information travels from peripheral receptors (e.g. in the skin) towards the DRG via the spinal nerve and then from the DRG to the dorsal horn via the dorsal rootlets.

Question 43

Do spinal nerves contain sympathetic fibres?

Answer 43

All 31 pairs of spinal nerves contain sympathetic fibres, which stimulate sweat glands and the contraction of smooth muscle in peripheral blood vessels and the hair follicles.

Question 44

What are dermatomes and myotomes?

Answer 44

A dermatome is the area of skin innervated by a single spinal nerve. Dermatome maps, like the one on the next page, show us the cutaneous territories of each spinal nerve. For example, sensation over the thumb is served by the C6 spinal nerve.

A myotome is the group of muscles innervated a single spinal nerve. In clinical practice, we assess the myotomes by asking the patient to move the joint associated with that muscle group and nerve.

Question 45

What is anastomosis and how is it helpful?

Answer 45

anastomosis - where branches from otherwise separate arteries unite with each other. Such an arrangement theoretically allows for the blood supply to an area to be maintained if one of the vessels supplying it becomes blocked.