Spinal Cord

Spinal Chord

• neural tissue originating from medulla oblongata

• protected by meninges

• 33 vertebrae forming the vertebral column

functions of the spinal chord

• relays information between body and brain

• communicates with rest of body through spinal nerves

• bypass brain → spinal reflex actions

structure of spinal chord (What does it contain)

• surrounded by white matter - myelinated, high lipid content

• H shaped inside part - grey matter, high concentration of cell bodies and dendrites

• dorsal root (one at the top),

• ventral root (one at the bottom)

  • dorsal root ganglion → Swelling in dorsal root due to aggregation of cell bodies

Passage of Neurons through the Spinal Cord

1. Sensory neurons enter through the dorsal root and have their cell bodies in the dorsal root ganglion.

   1. enters the dorsal horn in the grey matter where it synapses with interneurons which are unmyelinated allowing a decision to be taken

2. Motor neurons leave the cord through the ventral root, and are unmyelinated

reflex action

• rapid automatic response to a stimulus which is not under voluntary control of the brain

• these are not learnt → function is protection

• same stimulus same response

Cranial Reflexes

• sneezing, coughing, pupil dilation and blinking

Spinal Nerve Reflexes

• vasodilation

• vasoconstriction

  • peristalsis of the gut

reflex arc

• the pathway taken by a nerve impulses during a reflex action

→ monosynaptic

→ polysnaptic

monosynaptic

→ only one synapse

→ knee-jerk reflex - needed to walk

→ sensory neuron synapses directly to motor (quicker)

diagram of monosynaptic reflex

polysynaptic

→ more than 1 synapse

→ removing hand from hot object or pin

→ relay neurons are required between sensory and motor

ascending vs descending nerves

• ascending - carry sensory information to the brain

• descending - carry motor information away from the brain and to the spinal cord.