human physiology 100 - nervous system

What is sensory function?

Information carried from internal and external stimuli to CNS

What is integrative function?

Processes sensory information in the CNS

What is motor function?

Responds to integration by effecting a motor response

What is ganglia?

Are small balls of tissue where the cell bodies of sensory neurons are maintained, where information transfer occurs

What is the afferent division of the PNS?

- the incoming division
- carries sensory information from PNS sensory receptors to CNS

What is the efferent division of the PNS?

- the outgoing division
- carries motor commands from CNS to PNS muscles (smooth, skeletal, cardiac) and glands

What is the somatic nervous system?

- controls skeletal muscle contractions (voluntary)
- reflexes (involuntary)

What are the sympathetic and parasympathetic regions of the ANS?

- sympathetic : thoracic and lumbar region
- parasympathetic: cranial and sacral region

How do the sympathetic and parasympathetic nervous systems work together?

They have opposing effects meaning they have dual innovation/antagonistic control

What are the components of a neuron?

1. Cell body
2. Dendrites (receive information)
3. Axon
4. Synaptic terminals
5. Synapse (site of communication between neurons)

What are sensory neurons?

- afferent neurons of the PNS
- deliver information from sensory receptors to CNS
- somatic sensory neurons monitor outside conditions
- visceral sensory neurons monitor the bodies interior

What are the different types of sensory receptors?

- exoreceptors (outside)
- interoceptors (inside )
- proprioreceptors ( position and movement of skeletal and muscle joints)

What are motor neurons?

- efferent neurons of the PNS
- deceiver information from CNS to peripheral effectors
- somatic motor neurons innervate skeletal muscles
- visceral motor neurons innervate other effectors

What are interneurons?

- are association neurons
- are known as relay neurons as they receive signals/information from sensory neurons and transmit the information to motor neurones

What is neuroglia?

- it preserves the physical and biochemical structure of neural tissue that are essential to the survival and function of neurons
- make up 50% of neural tissue

What is the neuroglia of the CNS?

- ependymal cells
- astrocytes
- oligodendrocytes
- microglia

What are ependymal cells ?

- neuroglia of the CNS
- line central canal of spinal cord and ventricles of brain
- form epithelium called ependyma
- produce, secrete and monitor cerebrospinal fluid

What are astrocytes?

- largest and most abundant neuroglia in CNS
- maintain blood brain barrier
- repair damaged neural tissue
- guide neuron development
- control interstitual environment

What are oligodendrocytes?

- neuroglia of the CNS
- wrap around axons to form myelin sheaths
- smaller cell bodies with fewer processes

What are microglia?

- neuroglia of the CNS
- smallest and least numerous neuroglia with many fine branched processes
- clean up cellular debris, waste products and pathogens

What are the neuroglia of the PNS?

Schwann cells and satellite cells

What are satellite cells?

- neuroglia of the PNS
- regulate environment around neurons like astrocytes in the CNS

What are Schwann cells?

- neuroglia of the PNS
- form myelin sheaths around peripheral axons

What are the requirements for the membrane potential?

- plasma membrane is selectively permeable
- ion concentration differs in intercellular and extra cellular
- charge difference is maintained across plasma membrane (-70 mV)

What are the main membrane processes in neural activities?

- resting potential
- graded potential
- action potential
- synaptic potential
- information processing

What is the membrane potential?

- is the potential differing measured across a plasma membrane and expressed in millivolts
- results form the uneven distribution of positive and negative ions across the plasma membrane

What are passive channels?

- are always open
- leak channels
- membrane permeability changes in response to environment

What are active channels?

- are gated channels
- open and close in response to stimuli
- at resting potential most gated channels are closed

What are chemically gated channels?

- open or close when they bond to specific chemicals
- found on the dendrites and cell body of a neuron

What are voltage gated channels?

- open or close in response to changes in the membrane potential
- characteristic of areas of excitable membrane
- found in neuronal axons, skeletal muscle, sarcolema and cardiac muscle

What are mechanically gated channels?

- open or close in response to membrane distortion
- found in sensory receptors

What can a graded potential rise from?

- stimulation of a neurons sensory receptors (receptor potential)
- stimulation by another neuron via neurotransmitter (post synaptic potential)

What signal does a graded potential transmit?

Weak signals

What are:
1. Presynaptic excitation
2. Presynaptic modulation
3. Presynaptic inhibition

1. Presynaptic excitation : increased neurotransmitter release
2. Presynaptic modulation : the ability of passing on a signal might be affect because the release of a neurotransmitter
3. Presynaptic inhibition : decreased neurotransmitter release

What is summation?

A process where the effects of all graded potentials are integrated at one region of the plasma membrane

The combination of graded potentials can either be excitatory, inhibitory or both

What is inhibitory post synaptic potential (IPSP) ?

Hyperpolarises postsynaptic membrane moving further away from firing threshold
E.g -90mV

What is excitatory post synaptic potential (EPSP)?

Depolarises post synaptic membrane bringing closet to firing threshold
e.g 60mV

What are neuropeptides?

Neuromodulators that bind to receptors and activate enzymes

What are neuromodulators?

- chemicals released at synaptic knob that have similar function to neurotransmitters
- effects are long term
- can effect presynaptic membrane, post synaptic or both

What are inhibitory neurotransmitters?

- cause membrane hyperpolarisation
- inhibits the generation of action potentials
- contributes to muscle tone

What are excitatory neurotransmitters?

- cause membrane depolarisation
- promote the generation of an action potential

What are the steps of neurotransmission?

1. Action potential arrives at the axon terminal
2. Voltage gated calcium ion channels open
3. Calcium ions flow into cell
4. Synaptic vesicles dude with membrane and neurotransmitter released into cleft
5. Neurotransmitter diffuses to post synaptic terminal

What is an electrical synapse?

- located in the PNS and CNS
- rare
- direct physical contact at gap junctions
- ions move between cells through gap junctions
- held in position by binding between integral membrane proteins called connexions
- action potential is propagated quickly

What are the types of fibres and their rate of signal propagation?

- type A fibres: 12-130 m/sec, urgent information
- type B fibres: 15 m/sec, less urgent information
- type C fibres: 1 m/sec, less urgent information

What is salatory propagation?

- leap frog
- local current jumps from node to node on axons with myelin sheath
- is faster and uses less energy

What is the refractory period?

- the period during which the membrane will not respond to additional stimuli
- absolute : no action potential possible
- relative : very large stimulus can initiate an action potential

What are the steps to generating the action potential?

1. Depolarisation to threshold (-60 to -55 mV)
2. Activation of sodium channels and rapid depolarisation (+30 mV)
3. Inactivation fo sodium channels and activation of potassium channels (+30 mV)
4. Closing of potassium to temporary hyperpolarisation (-90 mV)

What are the four phases of the action potential?

- resting
- depolarisation
- repolarisation
- hyperpolarisation

What is the 'all or none' principle?

- if a stimulus reaches threshold, action potential is always triggered
- all action potentials are the same regardless so the stimulus

How will a nerve impulse be triggered by a graded potential?

If summation of graded potentials reach threshold at the axon hillock

What is a graded potential dependent on?

Is dependent on the stimulus in whether the threshold is reached or not

How to neuromodulators work?

- directly on membrane channels
- indirectly via G proteins (eg adrenaline)
- indirectly via intracellular enzymes (eg NO)