Somatic sensory nervous system

Conscious sensation pathways

-Integration center (the cerebral cortex which is responsible for conscious sensation and perception) - Afferent neurons- peripheral nerve, tract or pathway) - Sensory receptor (sensory stimulus converted into AP. Transduction).

Stimulus location: receptive feild

A region of space in which a stimulus can lead to activity in a particular afferent neuron. Small fields and dense innervation gives good discrimination between two points than larger less dense fields. For example comparing the back to the hand.

Somatotopic organisation

Areas of the cortex correspond to areas of the body, densely innovated areas have larger area of cortex as well as the cortex's innovating opposite sides.

Somatosensory cortex: sensation

Conscious identification of what and where in the primary region of the cortex, in the postcentral gyrus

Sensory information coding: Intensity

Frequency of AP firing in afferent neuron

Stimulus modality: slow chornic pain

Large receptive fields with small unmyelinated axon (B fibres) which produces visceral pain.

Stimulis modality: Proprioception

Length receptors which are muscle spindles that stretch reflex and shorten the muscle. Also responsible for posture of the person Tension receptors- function of length receptors and tension receptors. Golgi tendon organ- tension, relaxation as well as protection from tearing.

Sensory information coding: location

Location of sensory receptors which are mapped in the brain.

Somatosensory cortex: preception

Meaningful interpretation and association region of the brain.

Afferent Pathway for pain: Lateral spinothalamic Pathway:

Minimum of 3 neurons in relay which have interneurons as well as having the neurons going up and across. Starts at the primary sensory neuron,crossing to the opposite side to the collateral fibres to the reticular formation through the spinal cord the the somatic sensory area of the cerebral cortex.

Sensory receptors

Sensory endings of an afferent neuron or specialized receptor. The stimulus energy interacts with the end of the cell receptor which is highly sensitive. This message is then transferred onto a neuron which ends the message to the CNS.

Stimulus duration:

Sensory receptors are the most sensitive to change and often show adaptation which is the decreased receptor potential over time to a continuous stimulation. For example, like wearing clothes and not paying attention to it.

Stimulus modality: fast acute pain

Small receptive field with largish myelinated afferent axons (A fibres) and somatic pain.

Organization plan of the nervous system (Somatic nervous system)

Stimulus - Somatic and special receptors - somatic sensory division (afferent) - somatic integration centers - somatic motor division (efferent) - somatic effectors (skeletal muscle) - response.

Organization plan of the nervous system (Autonomic nervous system)

Stimulus - Visceral receptors - visceral sensory division (afferent) - Autonomic centers - Sympathetic division (efferent) -Parasympathetic nervous system both to autonomic effects (cardiac and smooth muscles/glands) - response.

Sensory information coding: duration

The duration at which the AP is firing in the afferent neuron.

Stimulus intensity- frequency in afferent neuron

There is a threshold which must be reached in order for a message to be transmitted and there to be a response. If it is not, there is no response in the afferent neuron until increasing stimulus will increase action potential frequency and the message it passed on.

Afferent pathway for touch and posture: Medial lemniscial (dorsal column pathway)

Three neurons in relay which goes up and across from the muscle spindles to the brain and are the fastest neurons in the body. Goes from primary sensory neuron into the spinal cord and synapases with the secondary sensory neuron which then crosses to the other side and up the spinal cord and mid-brain to the thalamus then finally to the somatic sensory area of the cerebral cortex.

Stimulus modality: Cells responsible for sensation of: Touch -Textural - Deep pressure/high frequency vibration - Light pressure - Low frequency vibration - Crude/persistant Pain

Touch -Textural- Krause's end bulb - Deep pressure/high frequency vibration- Pacini's corpuscle - Light pressure- Merkel endings - Low frequency vibration- Meissner's corpuscle - Crude/persistent- Ruffini's corpsule. Pain- Free nerve endings

Somatic and visceral sensations (inputs to the CNS which is direct and with the endocrine system)

Touch, pain, temperature and body position.

Sensory information coding: modality

Type of sensory receptor

Special senses (inputs to the CNS which is direct and with the endocrine system)

Vision, hearing, taste, smell and vestibular/balance