Spinal cord physiology

Function of white matter tracts

Highway for motor and sensory nerve impulse propagation

Function of grey matter

Receiving and integrating incoming/outgoing information

Reflex

Fast, involuntary, unplanned sequence of actions that occur in response to particular stimulus

Where do sensory neurones enter the spinal cord?

Dorsal horn - cell bodies in dorsal root ganglion

Where do motor neurones enter the spinal cord?

Ventral horn - cell bodies in ventral horn

Location of sensory neurone cell bodies vs motor neuorne cell bodies?

• sensory = dorsal root ganglion

• motor = ventral horn of spinal cord

Location of UMN

Cerebral cortex and brainstem

• axons remain in the CNS & synapse with LMN directly/indirectly

Location of LMN

In the brainstem and spinal cord

• axons leave the CNS to synapse with muscle fibres, making up final common pathway

What kind of neurotransmitter do alpha motor neurones relase?

ACh - acetylcholine

Where are alpha motor neurones found?

Ventral horn of spinal cord

Where do alpha motor neurones receive and integrate signals from?

• Muscle spindles (Ia afferents)

• Golgi tendon organs (Ib afferents)

• Cutaneous receptors

• spinal interneurons

• UMNs

Cause of MND?

Degeneration of a-motor neurones in the upper brainstem & lower spinal cord

Describe the basic reflex pathway

1. stimulus

2. sensory receptor

3. afferent sensory neurone

4. integration centre (CNS/spinal cord)

5. Efferent motor neurone

6. effector organ

7. response

Stretch reflex

Reflex causing contraction of skeletal muscle in response to stretching of the muscle (detected by muscle spindles)

Monosynaptic reflex

Single synapse between muscle sensory fibre and a-motor neurone

• eg; stretch refWhat is teh lex

What is the orientation of muscle spindle fibres to the muscle they are in?

They run parallel with muscle

Describe structure of muscle spindle

• intrafusal muscle fibres

• Ia sensory fibres

• y-motor neurone

Result of muscle spindle stretching

Increases Ia afferent activity

Where do Ia afferent sensory neurones synapse with the a-motor neurone?

Ventral horn of spinal cord

Roe of y-motor neurone in spinal reflex?

To regulate the sensitivity of sensory afferents to stretch

Example of stretch reflex?

Patella tendon reflex

Reciprocal inhibition

Inhibition of antagonist muscle to allow contraction of agonist muscle during stretch reflex

What is the inverse stretch reflex pathway protective against?

Muscle overload - preventing damage to muscles and tendons

Function of Golgi tendon organ?

Encodes and regulates muscle tension - protecting them form damage

Golgi tendon organ location?

Junction of muscles and tendons - running in series with extrafusal fibres

Innervation of Golgi tendon organs?

Ib afferent neurones

What activates Golgi tendon organs?

Force generated by muscle contraction acts directly on the tendon - increasing the tension of collagen fibrils in golgi organ.

• this causes compression of intertwined sensory receptors and increased activity of Ib afferents

In the inverse stretch reflex, what does the Ib afferent synapse with in the spinal cord?

Inhibitory interneurons

In the inverse stretch reflex, what impact does Ib activation have on a-motor neurones?

Decreases the activity of a-motor neurones

What is the basic principal or the inverse stretch reflex?

Up to a point, the harder a muscle stretched the stronger the contraction

• if tension is too much - contraction will stop suddenly and muscle will relax

Inverse stretch reflex

• Golgi tendon organ stimulated by high muscle tension

• Signals sent along Ib afferent fibres to spinal cord

• Ib synapse with inhibitory Ib interneurons = inhibiting a-motor neurones = muscle relaxes

• Simultaneously, excitory signals are sent to antagonist muscle promoting its contraction

What kind of reflex is the inverse flexor reflex?

Polysynaptic

what kind of neurone supplies afferent sensory information from nociceptor?

alpha-delta neurone

What are CPGs?

Produce complex rhythmic movements (eg: walking & running) without input from higher centres.

• neural networks that produce rhythmic patterned outputs without sensory feedback

Where are CPGs found?

Spinal cord and brainstem - consisting of sensory neurones, interneurons and motor neurones