Nerve Impulse & Synapse

3 types of stimulus

Internal
External
Energy source

2 types of receptors

Sense organs
Transducer

Do sensory systems have afferent or efferent pathways

Afferent

Afferent direction

Afferent is anything that collects information and send it to the CNS

Do motor systems have afferent or efferent pathways

Efferent

Role of receptors

Receptors collect data and convert it to the language of the nervous system

Role of somatic senses

Enables body to feel, ache, chill
Responsible for touch and pain

How does the nose detect smell

Hairs are connected to afferent neurons

Nose converts chemicals to action potentials

Receptors of somatic senses location

Broadly distributed

How specific are receptors for somatic senses

Not very- they respond to many kinds of stimuli

Role of somatosensory pathway

Convey type and location of the sensory stimulus

Somatosensory pathway neuron roles

Typically 3 neurons involved:

1. Primary sensory afferent neurons

2. Receptor (sensory neuron)(goes to the thalamus)

Neurons 1 gets it to the spinal cord

Neuron 2 gets it to the thalamus

Neuron 3 gets it to the cortex

Role of thalamus

The thalamus is a sorting centre (recognises where the signal is coming from and its frequency

Where do cell bodies of all sensory neurons sit

Dorsal route ganglia

Internal stimuli of somatic senses

Touch
Temperature
Pain
Itch
Proprioception
Pathway

The amount of space on the sensory cortex devoted to each body part is proportional to what?

The sensitivity of that part of the body

Sensory signals from the left side of the body go to what part of the brain

Right cerebral hemisphere and sensory areas of cerebral cortex

What stimulus modality & location is linked to what sensory receptor

is there ever any overlap of receptive fields of sensory units responding to different modalities

yes, often

Stimulus associated with rods & cones

Light

Adequate stimulus

The stimulus to which a specific receptor is specifically sensitive

Can sensors respond to stimuli that aren’t their adequate stimuli

Yes

For the eyes the adequate stimulus is light

This doesn't mean the receptors can't respond to other stimulus but it's best at recognising its adequate stimulus

4 steps for generating a sensation

Ion channels in specialised receptor membranes open/close for stimulus

Current flows through ion channels (creates graded change in membrane potential)

Action potentials are generated if receptor potential reaches threshold

Action potentials propagate along afferent neurons and cause release of neurotransmitter

Do primary sensory neurons fire action as stimulus is present?

Some do, others adapt

Adaptation of sensory receptors

Sensory receptors decrease in sensitivity to stimulus of constant strength (action potential frequency decreases)

Difference between rapidly adapting & slowly adapting sensory receptors

Rapidly adapting: Receptors signal changes in stimulus intensity
Slowly adapting: Receptors signal the continued presence of the stimulus

Example of a slowly adapting receptors

Pain receptors

What is AP (Action Potential) Propagation

How electrical signals travel along the axon of a neuron

Process of AP Propagation

Local current spread: ions spread along the axon, causing electronic conduction

Depolarisation of nearby part of membrane

A spike is initiated

How many directions can axons fire in

Can fire in both directions but typically fire in 1

Unmyelinated axon AP propagation happens by ________ conduction

Continuous

Myelinated axon AP propagation happens by ________ conduction

Saltatory conduction

1. Action potentials

2. Axon terminal

3. Synaptic vesicle

4. Docking Protein

5. Voltage gated Ca²⁺ channel

6. Postsynaptic cell

7. Receptor

Where are neurotransmitter molecules synthesised & packaged

Vesicles

Where in a chemical synapse does an action potential first arrive

Presynaptic terminal

When an action potential arrives at the presynaptic terminal and the Ca2+ channels open, what direction does the Ca2+ go

Enters the synapse

What does a rise in Ca2+ trigger

Fusion of synaptic vesicles with the presynaptic membrane

Where do transmitter molecules go

Diffuse across the synaptic cleft and bind to specific receptors on the postsynaptic cell

What activates the post synaptic cell

Bound receptors

Fate of neurotransmitter after post synaptic cell is activated

Breaks down

Is taken up by the presynaptic terminal / other cells / diffuses away from the synapse

Effect of EPSP (Excitory post synaptic potential) & IPSP (Inhibitory post synaptic potential)

EPSP increases likelihood of a polarising change in PSP

IPSP decreases likelihood of a polarising change in PSP

Is this an excitatory transmission or an inhibitory transmission

Excitatory

Is this an excitatory transmission or an inhibitory transmission

Inhibitory