CNS organisation and function

Question 1

Know the overall organisation of the nervous system

Answer 1

• Two branches, CNS and PNS
• CNS: brain and spinal cord
• PNS: neural tissue outside of the CNS

Question 2

List the parts of the spinal cords

Answer 2

• 8 cervical segments
• 12 thoracic
• 5 lumbar
• 5 sacral
• 1 coccygeal

Question 3

Understand the composition of the brain in terms of white matter and grey matter

Answer 3

• White matter: nerve fibres (white due to myelination)

* Grey matter: nerve cell bodies

Question 4

Know the major function of the lobes of the cerebrum

Answer 4

• Frontal lobe: problem solving, memory, judgement, social behaviour
• Parietal lobe: sensory information of taste, touch and smell. Hand- eye coordination, movement
• Temporal lobe: hearing and language
• Occipital lobe: visual perception

Question 5

Describe the somatosensory cortex and the primary motor cortex in terms of their location and function

Answer 5

• There are two parts of the brain; one controls sensory input and the other controls motor input

• The sensory input part is located in the parietal lobe and is known as the primary somatosensory cortex
• Somatosensory cortex: represents a map of brain areas dedicated tosensoryprocessing for different anatomical divisions of the body
• The motor input part is located in the frontal lobe. It is known as the primary motor cortex
• Primary motor cortex: represents a map of brain areas dedicated tomotorprocessing for different anatomical divisions of the body

Question 6

Be aware of the various sensory modalities and how they are transmitted to the brain

Answer 6

• Myelinated neuron fibres transmit signals very fast, whereas non- myelinated nerves transmit signals very slowly
• Myelinated fibres: The ability to touch, feel vibrations and possess proprioception
• Unmyelinated fibres: pain and temperature

Question 7

Be aware of how movement is controlled by the brain

Answer 7

• The primary motor cortex’s role is to generate neural impulses that control movement
• Signals from the PMC cross the body’s midline to activate skeletal muscles on the opposite side of the body
• If movement is required in the head and neck region, then it will enter the corticobulbar pathway where signals are sent to the brainstem to cause movement
• If anything else needs to be moved, it will enter the corticospinal tract where signals are sent to the spinal cord to cause movement of the body

Question 8

Define:

• Dermatome
• Myotome
• Decussation
• Homunculus

Answer 8

• Dermatome: an area of skin is mainly supplied by a single spinal nerve
• Myotome: the group of muscles that a single spinal nerve innervates
• Decussation: signals crosse the other side of the body. For example, the sensation from the right side of the body travel to the spinal cord and at the brain stem they cross over, thus the signal goes to the left side of the brain
• Homunculus: a distorted representation of the human body, based on a neurological “map” of the areas and proportions of the human brain

Question 9

Describe the conduction of a nerve impulse

Answer 9

• Each neuron receives thousands of neural impulses transmitted by different types of neurotransmitters
• Neurotransmitters can be excitatory or inhibitory. They can bind to a transporter in a following neuron to either allow depolarisation of the neuron or block depolarisation of the neuron
• In the event of depolarisation, the resting potential is shifted from -70 mv to 40 mv
• This occurs when large amounts of positive Na+ move into the cell
• As the electrical gradient of the cell moves towards 30mv, voltage gated channels open, allowing potassium to leave the cell
• This will cause repolarisation; the resting membrane potential will go back to being negative

Question 10

Understand the reflex arc

Answer 10

• A reflex action is an involuntary and nearly instantaneous movement in response to a stimulus
• A reflex arc is the pathway by which a reflex travels; stimulus -> sensory neuron -> synapse at spinal cord -> relay neuron -> motor neuron -> movement
• The relay neuron synapses with a motor neuron
• Because this arc bypasses the brain (the sensory neuron info doesn’t travel to the brain but to the synapse instead) it is very quick
• The brain receives sensory input as the reflex action occurs

Question 11

Understand the Gate control theory

Answer 11

• Pain signals are not free to reach the brain as soon as they are generated
• They need to encounter certain ‘neurological gates’ at the spinal cord level and these gates determine whether the pain signals should reach the brain or not
• Thus, pain is perceived when the gate allows the pain signals to reach the brain
• Moreover, when you get hurt you rub yourself. Sometimes the neurone responsible for conveying pain may also be responsible for other impulses
• Thus, there is an overcrowding of impulses in the brain which may have the effect of dampen the severity of the pain felt