Spinal reflexes

The reflex arc

The reflex arc

An automatic, rapid response to an adverse stimulus.

Action is involuntary the brain is not involved in the event but may be informed of it

Many reflex actions are protective Some complex actions (swallowing, coughing

and blinking) are coordinated by reflexes.

A simplified reflex arc

stimulus

A simplified reflex arc

stimulus

receptor

A simplified reflex arc

stimulus

receptor

sensory neurone

A simplified reflex arc

stimulus

receptor

sensory neurone

spinal cord of central nervous system

A simplified reflex arc

stimulus

receptor

sensory neurone

spinal cord of central nervous system

relay neurone

A simplified reflex arc

stimulus

receptor

sensory neurone

spinal cord of central nervous system

relay neurone

motor neurone

A simplified reflex arc

stimulus

receptor

sensory neurone

spinal cord of central nervous system

relay neurone

motor neurone

effector

A simplified reflex arc

stimulus

receptor

sensory neurone

spinal cord of central nervous system

relay neurone

motor neurone

effectorresponse

A withdrawal reflex

A withdrawal reflex

The stimulus is the heat from the hot object

A withdrawal reflex

The stimulus is the heat

from the hot object

The stimulus is detected by receptors in the dermis of the skin. Since these sensory cells respond to temperature, they are called thermoreceptors.

A withdrawal reflex

The stimulus is the heat

from the hot object

The stimulus is detected by receptors in the dermis of the skin. Since these sensory cells respond to temperature they are called

thermoreceptors.

The thermoreceptors initiate nerve impulses that pass to the spinal cord along a sensory neurone.

A withdrawal reflex

The stimulus is the heat

from the hot object

The stimulus is detected by receptors in the dermis of the skin. Since these sensory cells respond to temperature they are called

thermoreceptors.

The thermoreceptors initiate nerve impulses that pass to the spinal cord along a sensory

neurone.

sensory neurone cell body

A withdrawal reflex

The stimulus is the heat

from the hot object

The stimulus is detected by receptors in the dermis of the skin. Since these sensory cells respond to temperature they are called

thermoreceptors.

The thermoreceptors initiate nerve impulses that pass to the spinal cord along a sensory

neurone.

sensory neurone cell body

grey matter (neurone cell bodies)

A withdrawal reflex

The stimulus is the heat

from the hot object

The stimulus is detected by receptors in the dermis of the skin. Since these sensory cells respond to temperature they are called

thermoreceptors.

The thermoreceptors initiate nerve impulses that pass to the spinal cord along a sensory

neurone.

sensory neurone cell body

grey matter (neurone cell bodies)

spinal cord

A withdrawal reflex

The stimulus is the heat

from the hot object

The stimulus is detected by receptors in the dermis of the skin. Since these sensory cells respond to temperature they are called

thermoreceptors.

The thermoreceptors initiate nerve impulses that pass to the spinal cord along a sensory

neurone.

sensory neurone cell body

grey matter (neurone cell bodies)

spinal cord

white matter (neurone axons)

A withdrawal reflex

The stimulus is the heat

from the hot object

The stimulus is detected by receptors in the dermis of the skin. Since these sensory cells respond to temperature they are called

thermoreceptors.

The thermoreceptors initiate nerve impulses that pass to the spinal cord along a sensory

neurone.

sensory neurone cell body

grey matter (neurone cell bodies)

spinal cord

white matter (neurone axons)

The sensory neurone enters the spinal cord via the dorsal branch of the spinal nerve and forms a synapse with a relay neurone, inside the grey matter

A withdrawal reflex

The stimulus is the heat

from the hot object

The stimulus is detected by receptors in the dermis of the skin. Since these sensory cells respond to temperature they are called

thermoreceptors.

The thermoreceptors initiate nerve impulses that pass to the spinal cord along a sensory

neurone.

sensory neurone cell body

grey matter (neurone cell bodies)

spinal cord

white matter (neurone axons)

The sensory neurone enters the spinal cord via the dorsal branch of the spinal nerve and forms a synapse with a relay neurone, inside the grey matter

The short relay neurone forms a synapse with a motor neurone that leaves the spinal cord via the ventral root of the spinal cord.

A withdrawal reflex

The stimulus is the heat

from the hot object

The stimulus is detected by receptors in the dermis of the skin. Since these sensory cells respond to temperature they are called

thermoreceptors.

The thermoreceptors initiate nerve impulses that pass to the spinal cord along a sensory

neurone.

sensory neurone cell body

grey matter (neurone cell bodies)

spinal cord

white matter (neurone axons)

The sensory neurone enters the spinal cord via the dorsal branch of the spinal nerve and forms a synapse with a relay neurone, inside the grey matter

The short relay neurone forms a synapse with a motor neurone that leaves the spinal cord via the ventral root of the spinal cord.

The motor neurone carries the impulse to an effector, in this case muscles in the arm, which contract to withdraw the hand from the hot object. This action is known as the response.

A withdrawal reflex

The stimulus is the heat

from the hot object

The stimulus is detected by receptors in the dermis of the skin. Since these sensory cells respond to temperature they are called

thermoreceptors.

The thermoreceptors initiate nerve impulses that pass to the spinal cord along a sensory

neurone.

sensory neurone cell body

grey matter (neurone cell bodies)

spinal cord

white matter (neurone axons)

The sensory neurone enters the spinal cord via the dorsal branch of the spinal nerve and forms a synapse with a relay neurone, inside the grey matter

The short relay neurone forms a synapse with a motor neurone that leaves the spinal cord via the ventral root of the spinal cord.

The motor neurone carries the impulse to an effector, in this case muscles in the arm, which contract to withdraw the hand from the hot object. This action is known as the response.

A few reminders!

The central grey matter contains the cell bodies of relay and motor neurones.

The outer white matter contains myelinated axons, which run up and down the spinal cord to and from the brain.

In the centre of the grey matter is the spinal canal, through which the nutritive cerebrospinal fluid cirulates.

A few reminders!

Sensory neurones enter the spinal cord through the dorsal root and the concentration of their cell bodies forms a swelling called the dorsal root ganglion.

Motor neurones leave the spinal cord via the ventral root.