Lecture 11

Question 1

somatic pathway

Answer 1

Neural pathway that transmits sensory information from the body, including touch, pain, temperature, and proprioception, to the brain. It also carries motor commands from the brain to the skeletal muscles, enabling voluntary movement. Always excitatory (making muscles contract). At NMJ, it is being depolarised for excitation and neurotransmission is mediated by nicotinic acetylcholine receptors. Can be voluntary or involuntary (reflexes)

Question 2

Classification of neural reflexes

Answer 2

classified by
1) the effector controlled by the efferent division
2) The integrating region in the CNS
3) Time at which reflexes develops
4) Number of neurons in the reflex pathway

Question 3

Monosynaptic reflex

Answer 3

1) Stimulus activates receptor
2) Receptor sends signals through sensory neuron to spinal cord
3) Signal forms synapse in spinal cord with the somatic motor neuron
4) Somatic motor neuron sends signals to skeletal muscles

Question 4

Polysynaptic reflexes

Answer 4

1) Stimulus activates receptor
2) Receptor sends signals through sensory neuron to spinal cord
3) Signal forms synapse in spinal cord with the interneuron which then passes it onto another neuron
4) Neuron sends signals to skeletal muscles

Question 5

motor units

Answer 5

single motor neuron plus all the fibres it innervates

Question 6

alpha motor neuron

Answer 6

somatic motor neurons that innervate skeletal muscle contractile fibres.

Question 7

components of skeletal muscle reflexes

Answer 7

• proprioceptors (sensory receptors within muscle)
• CNS integration of signal
• alpha motor neurons: carry the output signal
• Extrafusal muscle fibres: effectors

Question 8

golgi tendon organs

Answer 8

Respond to muscle tension. They are located at the junction between muscle and tendon, where they are linked to the tendon and muscle fibers. These receptors are sensitive to changes in muscle force, not length. During contraction, the force is transmitted to collagen fibers within the tendon. Sensory neurons interwoven among these collagen fibers become compressed or stretched, causing them to fire action potentials. This sensory input is sent to the spinal cord, where it can trigger inhibitory reflexes to prevent excessive force that might damage the muscle or tendon.

Question 9

Muscle spindles

Answer 9

Respond to muscle stretch. They are embedded within skeletal muscles, with multiple spindles located among the muscle fibers. Each spindle contains intrafusal muscle fibers, which have a central non-contractile region (lacking actin and myosin), wrapped by sensory neurons. This region is sensitive to stretch. Contractile ends, which are innervated by gamma motor neurons. These allow the spindle to adjust its sensitivity during movement. Sensory neurons in the spindle are tonically active, meaning they constantly fire at a baseline level. When the muscle stretches, firing rate increases. These sensory neurons synapse in the spinal cord with alpha motor neurons, triggering a reflex contraction (the stretch reflex) to resist further stretching and maintain muscle tone.

Question 10

stretch reflex

Answer 10

1. load is added and stretch reflex occurs
2. When another is added, the muscle spindles stretch and the muscle spindle afferents are firing more frequently
3. Reflex contraction initiated by muscle stretch restores arm position and prevents damage from overstretching

Question 11

alpha-gamma coactivation

Answer 11

Ensures muscle spindles remain sensitive during muscle contraction. When extrafusal muscle fibres (the main contractile fibres) are activated by alpha motor neurons, the gamma motor neurons activate the intrafusal fibres (inside the muscle spindle). This coordinated activation causes both the extrafusal and intrafusal fibres to contract. Because the intrafusal fibres contract along with the muscle, the central (sensory) region of the muscle spindle remains stretched, keeping the firing rate constant. This ensures that the muscle spindle can continue to detect any unexpected changes in muscle length. For example, if an external load is added during contraction, the muscle might be stretched more than expected. The constant firing, maintained by gamma activation, allows for a rapid reflex response to adjust muscle tension appropriately. The net effect of alpha-gamma coactivation is the maintenance of spindle sensitivity and constant sensory feedback during voluntary muscle movements, contributing to smooth and coordinated motor control.

Question 12

patellar reflex

Answer 12

1. tendon is tapped, stretching muscle
2. muscle spindle stretches and fires to spinal cord
3. Spinal cord receives excitatory signal and sends it down to gamma neuron on quadracepts. Also activates inhibitory interneuron
4. Quadracepts contracts while hamstring contraction is inhibited.

Question 13

Flexion and crossed extensor reflexes

Answer 13

Removes limb from painful stimulus via polysynaptic reflex.

1. Stimulus is detected by noiciceptors
2. Flexor muscles contracts, antagonistic muscles relax

Question 14

crossed extensor reflexes

Answer 14

compensatory change in other limb that retains posture.

Question 15

pain reflex sides

Answer 15

if stimulus on left foot, you stimulate the hamstring and relax the quadracep to lift up the leg and in the right leg, you stimulate the quadracept but relax the hamstring to shift weight. If stimulus in right foot, it swaps side.

Question 16

integration of reflexes

Answer 16

reflexes dont require input from cerebral cortex as usually spinal cord integrates stretch and flexion reflexes. Brain stem integrates postural reflexes and hand/eye movement. Cerebellum is involved in fine-tuning movements.

Question 17

Phases of voluntary movements

Answer 17

3 phases (planning, initiation and execution). Involved cerebral cortex, cerebellum and ganglia.

Question 18

Planning

Answer 18

1. You have a thought e.g going for a walk
2. Basal ganglia and cerebellum coordinate to send signal to the motor cortex

Question 19

Initiation

Answer 19

3. Motor cortex receives feedback to modulate what happens in cerebellum and basal ganglia

Question 20

Execution

Answer 20

4. Motor cortex generates movement
5. Movement has negative feedback impact on motor cortex to fine-tune processes as with the cerebellum and basal ganglia.

Question 21

Parkinson’s Disease

Answer 21

Loss of neurons in basal ganglia and hence, ability to initiate movement.

Question 22

feedforward

Answer 22

Preparation of voluntary movement

Question 23

feedback

Answer 23

Create smooth and continuous movement

Question 24

Purpose of feedback/feedforward

Answer 24

maintain posture during movement

Question 25

feedback/forward steps

Answer 25

1. Brain receives sensory input via sensory organ 2. sensory cortex sends signals to motor cortex and motor association areas. 3. when it reaches basal ganglia and thalamus, decision process occurs. 4. Response is coordinated where cerebellum and motor cortex sens signals to brain stem. 5. signal goes to spinal cord 6. response. Feedback through sensory receptors

Question 26

corticospinal tracts

Answer 26

Responsible for controlling voluntary movement, particularly fine motor control. Motor signals originate in the motor cortex and travel down through the midbrain to the spinal cord. If the signals are intended for the face or head, they are routed through cranial nerves via the corticobulbar tract. Otherwise, they continue to the medulla oblongata, where they cross over at the pyramids of the medulla. These crossed fibres descend in the lateral corticospinal tract and synapse with somatic motor neurons in the spinal cord to control muscles of the limbs.