Pain and Sensation - The SNS

Question 1

List the different types of sensory receptors.

Answer 1

ENCAPSULATED
Meissner corpuscles - Touch
Pacinian corpuscles - Pressure
Ruttini endings - Pressure
Krousse endings - Touch

UNENCAPSULATED
Root hair plexus - Touch
Free nerve endings - Pain, heat, cold
Merker discs - Touch

Question 2

Review how an action potential propagates along a nerve cell.

Answer 2

Sodium channels open, sodium floods in.Potassium channels open potassium flows out. Sodium potassium pump restores resting membrane potential (-70mv)

Question 3

Describe pain receptors, pain pathways, and the neurotransmitters involved.

Answer 3

Dendrites in periphery -> Peripheral axon in peripheral nerve -> Cell body in dorsal route ganglia -> Central axon and terminals in white matter in the spinal chord.

Question 4

Describe the anatomical relationship between the spinal chord and the vertebral column.

Answer 4

Spinal chord is within the spinal column. Pia mater, subarachnoid space, arachnoid mater, dura mater.

Question 5

Explain where spinal nerves exit the vertebral column.

Answer 5

Spinal nerves enter and exit at the top of the spinal chord (C3-T2) and bottom (L1-S3)

Question 6

Distinguish between motor and sensory nerves.

Answer 6

Sensory (afferent) from receptor to spinal chord

Motor (efferent) from spinal chord to rest of body

Question 7

identify the position of the somatosensory cortex and explain how it is arranged.

Answer 7

The somatosensory cortex is located in the post central gyrus of the parietal lobe of the brain. Contains thermoreceptors, chemoreceptors etc

Question 8

State the differences between chronic and acute pain.

Answer 8

Chronic pain serves no physiological purpose. It is when pain has lasted over 6months

Question 9

Describe the pathway that is involved in the transmission of pain from the periphery to the cerebral cortex.

Answer 9

nociceptor -> dorsal horn of spinal chord -> Spinothalamic tract -> Ventral posterior lateral nucleus in the thalamus -> Sensory cortex

Question 10

Describe the course of the sciatic nerve.

Answer 10

Pelvis -> Gluts -> Thigh -> Terminates by bifurcating into the tibial and common fibular nerve

Question 11

Define what is meant by a ‘slipped disk’ and how it can lead to symptoms such as sciatica.

Answer 11

When one of the discs in the spine ruptures and synovial fluid leaks out. Can trap nerves leading to sciatica

Question 12

Draw a cross section through the lumbar region of the vertebral column.

Answer 12

.

Question 13

Explain what is involved in a tendon jerk reflex

Answer 13

Tendon jerk reflex in response to pain via a reflex arc. No involvement of the brain

Question 14

Identify and list the special senses.

Answer 14

Vision
Hearing
Smell (olfacation)
Taste

Question 15

Describe how each of the special senses utilises the SNS to carry out its function.

Answer 15

VISION - eyes contain photoreceptors (rods and cones). Rods are the most numerous and work in dim light, cones require more light but provide colour vision. These synapse with sensory cells whose axons converge to form the optic nerve. Fovea contains only cone cells.
HEARING - Sound waves are collected by auricle and conducted through the external ear. Sound waves hit the tympanic membrane and cause it to vibrate. Vibration is transmitted and amplified through the ossicles. Vibration of stapes on oval window causes fluid in cochlea to vibrate. Vibrations stimulate the spiral organ (sensory receptor) which triggers action potentials in the vestibularchoclear nerve.
SMELL - Operants enter the nasal cavity and dissolve in the mucous. Presented to receptor proteins on olfactory epithelium. Olfactory nerve stimulated. Information transmitted to olfactory cortex.
TASTE - Taste buds contain approx 40 taste cells. Each taste cell possesses hair like projections which open onto the surface at the taste pore. Sensory receptors are located on the taste hair. Sensory axons leave the base of the taste bud in the cranial nerve.