PHSL231 Progress test 2

Primary afferent neuron

Synapses on 2 neuron

Where do axons cross over for pain and temperature (anterolateral pathway)

Low in the spinal cord

Where do axons cross over for fine touch and proprioception (dorsal column)

High in the spinal cord, in the medulla

What are the four types of sensory receptors of the skin

Thermoreceptors
Proprioceptors
Touch Receptors
Nociceptors

Thermoreceptors

Respond to changes in temperature
Are more active at warm or cold temperature ranges

Proprioceptors

Monitor the position of limbs (muscle spindles, golgi tendons, joint capsule)

Touch receptors

respond to mechanical stimulation of the skin

Nociceptors

Pain receptors, respond to extreme mechanical, temperature, and/or chemical stimuli

Pancinian Corpuscle

A type of mechanoreceptor cell which has nerve endings in the skin that are responsible for sensitivity to vibration and pressure

Where are mechanosensitive channels

At the first node of ranvier

Adaption in Pacinian corpuscle

The action potential decays, and action potentials stop
Results from receptor mechanical properties and axon ion channel properties

Four types of sensory coding

Modality
Intensity
Location
Duration

Modality

Specificity of receptors

Intensity (sensory coding)

Frequency of action potentials in each axon, number of axons activated

Location (sensory coding)

Mapping of receptive fields of individual primary afferents to specific cortical locations

Duration (sensory coding)

Receptors respond briefly even if stimulus is sustained. detect movement and changing pressure, wherease slow adapting receptors can signal true duration of stimulus

Anterolateral pathway

Ascending sensory pathway in the spinal cord and brainstem that carries information about pain and temperature to the thalamus.

Dorsal column pathway

ascending pathway for somatosensory information, fine touch and position; runs through dorsal area of spinal white matter

Lateral inhibition

The pattern of interaction among neurons in the visual system in which activity in one neuron inhibits adjacent neurons' responses.

What does lateral inhibition result in

Centre surround inhibition

Somatotopic representation in primary somatosensory cortex

Ordered representation of body where area is proportionate to density of receptors and use

Where are pain receptors found

Everywhere except the brain

Why is pain useful

To avoid injury, alert to infection and aid recovery
Can indicate disease elsewhere in the body

What are the two types of pain nerve fibres

C fibres and A fibres

C pain nerve fibres

Small diameter, unmyelinated, slow conduction velocity, signal ongoing damage

A pain nerve fibres

Small diameter, myelinated, faster conduction velocity, signal acute onset of painful stimulus

Why do pain pathways become more sensitive following injury

Sensitisation of sensory endings by locally releases factors
Changes at CNS synapses

Hyperalgesia

Increased sensitivity of pain pathways

Role of mast cells in pain response

Release histamine which recruits neighbouring axons to bring them closer to threshold, therefore making other ares more likely to be activated, giving a sensation of pain in uninjured areas

Gating of pain

Non painful stimuli of nearby nerves which provide pathway with more input, crowding it out

How do you gate pain

Rubbing affected area, or Trans-epidermal nerve stimulation (TENS)

Descending control

pathways to spinal cord form brain and brainstem also regulate pain transmission

Endogenous opiates

Released at synapses on pain-pathway neurons
acute response to pain and stress

Endocannabinoids

Synthesised and released by neurons
Decrease long term sensitivity to pain, act on pain receptors as well as centrally

Diabetic Neuropathy

Loss of sensation, including pain, can lead to tissue damage

Muscle pain

Related to tension, overuse or physical exercise
Involve surrounding tissue

Referred pain

pain that is felt in a location other than where the pain originates

How does referred pain occur

Cross talk of visceral and somatic sensory pathways

Neurogenic pain

Nerve compression can cause pain to be felt in region of nerve termination

Phantom limb pain

Pain felt in region that no longe exists

How does phantom limb pain occur

Ongoing activity of nerves that used to come from that part
or invasion of cortical representation for that part by intact body regions

What is the spinal cord involved in

Processing commands from brain
Reflexes
Rhythmic motor patterns

What generates basic patterns of rhythmic muscle activity

Spinal cord and brainstem circuits

What are basic patterns of rhythmic muscle activity used for

Locomotion
Breathing
Chewing
Swallowing

How does the primary motor cortex regulate spinal cord motor systems

via the corticospinal tract

Somatotopy in primary motor cortex

Body parts represented roughly sequentially across cortex
size of area is dependent on level of control and use

Corticospinal pathway

Output from motor cortex that controls spinal neurons, for fine, isolated movements (crosses to opposite side)

Brainstem pathway

Coordinated activity in large muscle groups, for posture, locomotion, routine activities (crossed and uncrossed)

What are the special roles of primary motor cortex

Controlling force of muscle contractions and direction of movements

What do most axons from motor cortex synapse on?

interneurons (not alpha motor neurons)

Bionic arm - how is motor program converted into action

EMG recording in muscle controls computerised muscles in arm
Intention of moving is pre-programmed behaviour/sequence

Basal ganglia loop

Sensorimotor cortex to basal nuclei to thalamus, to cortex

What occurs during preparation for movement

Basal ganglia loop
Keeps looping until it reaches substansia nigra, which releases dopamine and creates a positive feedback system

Roles of Basal Ganglia

Provides the background patterns of movement involved in voluntary motor activities.

What is needed for the initiation of movement

Basal ganglia

What causes parkinsons disease

Death of dopamine neurons - typically when about 70% have died

Parkinsons disease

Difficulty initiating movements and tremor

Role of Cerebellum

Helps plan, execute and learn motor programs
Integrates sensory information with planned motor programs

Asynergia (cerebellar injury)

Loss of coordination of motor movement

Dysmetria (cerebellar injury)

The inability to judge distance and when to stop

Adiadochokinesia (cerebellar injury)

The inability to perform rapid alternating movements

Intention tremor (cerebellar injury)

Movement tremors

Ataxic gait (cerebellar injury)

Staggering, wide based walking

Hypotonia (cerebellar injury)

Weak muscles

Ataxis Dysarthia (cerebellar injury)

Slurred speech

Nystagmus (cerebellar injury)

Abnormal eye movements

How many forms of input into the nervous system

four

How many forms of output in the nervous system

three

afferent division

carries sensory information from PNS sensory receptors to CNS

efferent division

carries motor commands from CNS to PNS muscles and glands

What are the three divisions of autonomic nervous system

Sympathetic autonomic pathway
Parasympathetic autonomic pathway
Enteric nervous system

Sympathetic autonomic pathway output

from spinal cord (thoracis through to lumbar)

Ganglia in sympathetic autonomic pathway

Chain that runs in parallel to spinal cord, called paravertebral ganglia

What is the exception of paravertebral ganglia in the sympathetic autonomic pathway

Adrenal ganglion. Releases adrenaline instead of noradrenaline

Parasympathetic autonomic pathway outout

Comes from brainstem

Vagus

Tenth cranial nerve in the parasympathetic system, branches multiple times and innovates body from top to bottom

Where is the first synapse in ANS sympathetic

Paravertebral and prevertebral ganglia

Where is the first synapse in AND parasympathetic

Is in or near the target organ

Enteric Nervous System (ENS)

neural tissue associated with the digestive system that is responsible for nervous control through autonomic connections

What is the ENS influenced by

Parasympathetic and sympathetic inputs, that indirectly increase and decrease intestinal activity respectively

How does the ENS control motility

By influencing smooth muscle excitability

What do local ENS reflexes do

Propel food along the gut

Contraction above (ENS)

Oral

Contraction Below (ENS)

Anal

What is the exception to contraction above being oral and contraction below being anal, switching

Vomiting

How does the local ENS reflex propel food along the gut

Serotonin is released, which activate sensory neurons which cause activation of excitatory motor neurons (orally) and activation of inhibitory motor neurons (anally)

What does an electroencephalogram (EEG) measure

Brain electrical activity which corresponds to synaptic potentials

What are EEGs used for

Monitor behavioural state, diagnose epilepsy, localise brain areas active in different tasks

Alpha waves

The brain waves which oscillate at a particular frequency whilst sitting down with eyes closed

Magneto-reception in humans

Can detect magnetic field, as EEG shows lack of alpha waves when activated

REM sleep

Rapid eye movement

What occurs whilst in REM sleep

Muscular movements are relaxed which allows dreaming without motor output so sleepwalking does not occur

What occurs to body during REM

Resembles waking state - brain becomes more active, heart rate and respiration go up

suprachiasmatic nucleus (SCN)

Generates sleep waking cycle of about 24 hours even in complete darkness

Orexins

Proteins that the hypothalamus releases to keep us awake

Narcolepsy

Lack or defective orexin neurons cause unexpected sleep

Functions of sleep

Recuperation and homeostatic housekeeping
Energy Saving
Memory consolidation

Functions of dreaming

learning, memory, emotional processing

What is consciousness

Able to immediately respond to environment

Unconsciousness - Coma

Unable to be roused, disordered brain state