3: The Central Nervous System

Question 1

Integration of the Spinal Reflexes

Answer 1

Sensory information comes in via the sensory neurons through the dorsal root. Interneuron integrates the information and a motor response exits through the ventral roots via the motor neurons.

Question 2

Spinal Cord: Crude Touch, Temperature and Pain

Answer 2

• CTP: crude touch, temperature and pain
• Spinothalamic tract takes sensory information regarding CTP up to the thalamus so the thalamus can send info to the important areas
• Crosses at the level at which it enters

Question 3

Spinal Cord: Touch and Proprioception

Answer 3

• Dorsal column
• Information ascends immediately and doesn’t cross until it gets up to a much higher level around the level of the brain stem

Question 4

Spinal Cord: Voluntary Movement

Answer 4

• Corticospinal tract: from cortico to spine
• Motor message
• Crosses over quite high near brain stem, descends and enters the corticospinal tract, exits via the ventral root

Question 5

Venous Drainage from the Brain

Answer 5

• All the blood taken up to the brain is drained via the venous system
• Exits via the jugular vein on the way to the heart once it has been deoxygenated in the brain

Question 6

Protection of the Brain’s Blood Supply: Centrally

Answer 6

The brain always gets a constant supply of blood except for when cardiac output can’t handle it or when there’s a rise in inter cranial pressure.

Question 7

Protection of the Brain’s Blood Supply: Locally

Answer 7

• Modulated by the Circle of Willis
• If the middle cerebral artery get blocked (thrombus), we can still get blood around the rest of the brain via some of the other collateral circulations

Question 8

The Meninges: Seatbelts for the CNS - Sub-Dural Space

Answer 8

• Potential space

- Only a space when something gets in there

Question 9

The Meninges: Seatbelts for the CNS - Sub-Arachnoid Space

Answer 9

• Actual space

- Where all the blood vessels are located

Question 10

The Meninges: Seatbelts for the CNS - Dural Folds

Answer 10

• Falx cerebri: runs anterior and helps separate the two hemispheres
• Tentorium: separates the cerebrum from the cerebellum
• Locks the brain in place so it’s not moving around and bouncing off of the skull
• Support and restraint

Question 11

Cerebrospinal Fluid

Answer 11

• Airbags of the CNS

- CSF in brain is constantly being made, circulates around and then is drained out with the deoxygenated blood

Question 12

Blood-Brain Barrier: How is it Formed?

Answer 12

• Astrocytes: they wrap around the capillary and modulate what is allowed to come in and out
• Keeping the environment (CSF) stable

Question 13

Blood-Brain Barrier: Crossing

Answer 13

• Small lipophilic molecules

- Molecules which have specific transporters e.g. glucose, amino acids

Question 14

Blood-Brain Barrier: Things that Can’t Cross

Answer 14

• Various types of charged particles, other large molecules, immune cells

Question 15

Blood-Brain Barrier: Things that Open the BBB

Answer 15

• Microwaves
• Radiation
• Trauma
• Hypertension
• Infection

Question 16

Problems Created by the Protective Coverings of the Brain

Answer 16

• The cranium can’t expand
• If anything adds to the volume of the cranial contents - increase in intercranial pressure
• Things that would add to the volume:
  > Oedema
  > Abscess
  > Tumour
  > Space-occupying lesions

Question 17

What Happens when a Space-Occupying Lesion Develops?

Answer 17

1. CSF forced out of the cranium
2. Less blood flows into the brain as the increased pressure inhibits in-flow
3. Structures in the brain are compressed - herniations of tissue

Question 18

Classic (Late) Signs of Raised ICP

Answer 18

• Deep, irregular respiration
• Widening pulse pressure
• Bradycardia
• Known as “Cushing’s Triad”

Question 19

The Brainstem: Pons

Answer 19

• Has a lot of connections with the cerebellum
• Acts as a relay centre
• Gets a lot of information from the cortex and will send it to the cerebellum

Question 20

The Brainstem: Functions

Answer 20

• Level of alertness
• Basic survival functions:
  > Respiration
  > Maintenance of BP
• Controls breathing and heart beat

Question 21

The Cerebellum

Answer 21

• Coordination and control of voluntary movements
• Postural adjustment during movements
• Advance planning of rapid movements
• Learning of movement sequences
• Helps provide smooth, coordinated body movement

Question 22

The Limbic System

Answer 22

• Number of structures clustered around the brainstem
• Motivation (emotions) for survival purposes
• Learning and memory
• Linking of autonomic and endocrine responses to emotional states
• 4 Fs of survival: fighting, fleeing, feeding and fornicating

Question 23

The Amygdala: Hub of Fear and Aggression

Answer 23

• Emotional learning: association of a sensory experience with an emotion (usually fear)
• Allows recognition of fear in others (facial expressions)
• Is strongly activated during exposure to aversive stimuli (visual, taste, auditory, smell)

Question 24

People with Damage to Both Amygdala

Answer 24

• Do not show fear to stimuli that normally provoke a fear response
• Are unable to make risk assessments: benefit estimates and tend not to avoid an activity when the risk outweighs the benefit
• Are unable to recognise fearful expressions on faces
• Avoid eye contact during social interactions and stand closer to others during contact

Question 25

Functions of the Hippocampus

Answer 25

• Conversion of short-term memory

- Memory for place