Reflexes

crossed extensor reflex

when a withdrawal reflex is initiated in one lower limb, the crossed extensor reflex causes extension of opposite lower limb

What is the role of the Golgi tendon organ and its reverse myotatic reflex?

- Prevents damage due to overwork - Provides fine control of muscle

What are the neural components in a reflex arc?

- Sensory receptor - Afferent neurone - Integration centre (involved interneurones which are found in-between sensory and motor neurones in the CNS and enteric NS) - Efferent neurone - Effector

What are the general functions of reflexes?

- protective (e.g. limb withdrawn and the cough reflex) - postural control (e.g. walking) - homeostasis (e.g. blood pressure)

Reflex

A simple, automatic response to a sensory stimulus, such as the knee-jerk response Involves somatic and autonomic neurons

Describe the withdrawal reflex

Receptors in the skin activate a AP that travels to the interneurons in the spinal cord. There are lots of interneurones that are either inhibitory or excitatory Inhibitory interneurones do not stimulate the efferent neurones, so less ACh release at the extensor muscle, causing it to relax Excitatory interneurones stimulate efferent neurones, causing Ach release at the flexor muscle, causing it to contract This occurs simultaneously in both left and right limbs This allows us to remove the limb from the source of pain while adjusting body posture (plant other leg down) to prevent us falling over

A reflex is ..., .... and ....

Stereotypes - predictable Involuntary Rapid

Describe the simple stretch reflex (myotatic) involving the muscle spindle

Stimulus causes the muscle spindle to stretch. This also causes the nerve ending to stretch, enabling the receptor potential to reach the threshold so that an AP is generated. This is an excitatory synpase and excitatory NT are released. This then travels along the afferent neurone to the spinal cord. This is mono-synaptic so there are no interneurones in the CNS. This afferent neurone synapses with the efferent/motor neurone causing Ach to be released, causing muscle contraction.

Describe the knee jerk reflex

Stimulus is given where the tendon to the quadriceps is, that stretches the spindle, activating the sensory neurone. This sensory afferent synapses with the efferent neurone, releasing an excitatory neurotransmitter, causing the quad to contract There is an interneuron which releases inhibitory neurotransmitters which stops the motoneurons form firing. This causes the hamstring to relax This produces the knee jerk movement

How does the Golgi tendon organ prevent overwork?

The muscle contracts, which results on a pull on the tendon This straightens collagen fibres, which causes mild compression to the sensory nerve ending, activating the Golgi tendon organ The AP in the sensory afferent enters the spinal cord and an excitatory neurotransmitter is release to the inhibitory interneurone. The activity of this inhibitory neurone then increases, but because it releases inhibitory neurotransmitter, it inhibits the activity of the efferent neurone. So Ach release at the muscle stops No contraction

Describe the withdrawal reflex

When a person touches something painful, receptors in the skin send impulses to interneurons in a reflex center in the spinal cord. The reflex center sends impulses to the flexor muscles of the affected part causing the part to be moved away. At the same time this is happening, impulses to the extensor muscles of the affected part are inhibited, so that the flexors can work more effectively. A phenomenon, called a crossed extensor reflex, occurs simultaneously with the initial reflex that causes the extensors of the opposite limb to contract.

the golgi tendon organ is.... which means that...

is polysynaptic -which means the one or more interneurones are connecting sensory afferent and motor efferent.

increase in contraction....

prevents damage

what type of receptor is a golgi tendon organ

proprioceptors

Muscle spindles

receptors buried in the muscle sensitive to change in length of the muscle and the rate of that change -they sense muscle stretch