Animal Flashcards
What is the function of the nervous system?
Sense and respond to environment. Coordinate movement. Regulate internal functions of the body.
What do Neurons do?
Receive and transmit information
What do dendrites do?
Recieve
What do axons do?
Transmit.
What do neurons use to transmit?
Electrical signal
What is membrane potential?
Charge difference between inside and outside of the cell
What is the resting membrane potential?
Inside more negative. -70mV - known as polarised.
How is the resting membrane potential achieved?
- 3 Na+ out, 2 K+ in
- Changes conc.
- Some of the K+ move out through leak channels, down their concentration gradient
- Makes the inside more negative
What would happen if the membrane was more permeable to Na+?
Na+ ions would move inside until equilibrium is reached
What is the electrochemical equilibrium for Na+?
+60mV
What is the electrochemical equilibrium for K+?
-90mV
Where are action potentials generated?
Axon initial segment
How are action potentials generated?
- Depolarization
- If threshold is reached ion channels open
- Influx of Na+ ions
- Further depolarization (positive feedback)
How is the resting potential regained after an action potential?
- Ion channels soon close and remain inactive for a while
- Potassium channels have a delayed response and then open
- K+ ions move out
- Potential decreases going below resting potential
- Ion channels restore concentrations
- Resting potential is restored
How are action potentials propagated along the axon?
- Increase in positive charge inside axon
- Na+ move to neighboring regions
- Leads to depolarization
- If above threshold there will be full depolarization
- Moves from section to section
Why does the action potential not move backwards?
Refractory period and synapses
What is the absolute refractory period?
All sodium ion channels are either closed and inactivated or are already open. No action potential can be generated
What is the relative refractory period?
Inactive or normally close. Potassium also open.
What does the speed of the action potential depend on?
Axon diameter and myelination
What is the effect of a bigger axon diameter on an action potential?
Lower resistance to charged molecules. Can move faster. Therefore faster conduction velocity.
What is the effect of myelination on action potential?
Conduction velocity higher. fast. Energy efficient.
What are myelin sheaths made from?
Glial cells either Schwann cells or oligodendrocytes. Lipid rich layers
What are Schwann cells?
Found in the Peripheral NS and the whole cells wrap around the axon
What are Oligondendrocytes?
Found in the Central NS and cell forms extensions which wrap around
What are nodes of Ranvier?
Small gaps in the myelin sheath
What do myelin sheaths do?
Electrically insulates - reduce charge that can move across
What would happen with no myelination?
Voltage gated ions would need to be close together so they don’t lose depolarization and drop below threshold level
What does Saltatory Conduction do?
Reduces charge lost across membrane and reduces decay of depolarization over distance. Energy efficient - less action potentials - less work for sodium and potassium-ases
How are signals transmitted to other cells?
Via synapses
How do synapses transmit signals?
Majority are chemical
Explain the process of signal transmission at a chemical synapse?
- Depolarization arrives at axon terminal leading to the opening of voltage gated calcium ion channels
- Influx of Ca2+
- Increased conc leads to fusion of vesicles with plasmembranes
- Neurotransmitters are released into the synaptic cleft
- Bind to receptors on postsynaptic membrane
- Binding leads to opening of ion channels
- Sodium ion channel opens
- Neurotransmitters diffuse away or are broken down
What is an EPSP?
Excitatory postsynaptic potential - can lead to action potential if over threshold
What does a weak EPSP mean?
Small depolarisation - doesn’t reach threshold - no action potential
What is Temporal Summation?
- EPSP doesn’t reach threshold
- Second and third arrive in quick succesion
- First one has not disappeared yet so they combine
- Summed EPSP reach the threshold
What is Spatial Summation?
- EPSP stimulated from different synapses
- Neurons can receive from multiple neurons
- If fired together they can combine and reach the threshold
What are IPSPs?
Inhibitory Postsynaptic Potentials
How do IPSPs work?
- Depends on ion channels that open
- Potassium channels open or chloride channels open
- Leads to hyperpolarization and inhibits generation of an action potential
What are some examples of EPSP neurotransmitters?
Acetylcholine. Glutamine.
What are some examples of IPSP neurotransmitters?
Glycine. GABA.
What are the 3 types of neuron?
Sensory. Interneuron. Motor.
Describe the structure and function of the sensory neuron?
Usually pseudounipolar. Information about environment or internal physiological state. Transmit to interneuron.
Describe the structure and function of the interneuron?
Usually multipolar. Process information. Transmit to the motor neuron.
Describe the structure and function of the motor neuron?
Usually multipolar. Produces suitable responses to the signals received.
What is meant by multipolar?
Several processes originate at the cell body. Several dendrites, one axon. Number of dendrites can vary. Shape of multipolar can vary.
What is meant by bipolar?
One dendrite that branches, One axon that branches.
What is meant by Pseudounipolar?
Axon that forms 2 main branches. Cell body between them.
How are neurons organised in the brain?
Centralized information. Processing group of neurons.
How are neurons organised in the ganglion?
Group of nerve cell bodies. processes information from local region.
How are neurons organised in the Nerve and Nerve cord?
Collection of bundled axons.
What is the human nervous system split into?
CNS and PNS
What does the CNS consist of and what is its role?
Spinal Cord. Brain. Mainly interneurons. Sensory to CNS. CNS to motor to muscles
What does the PNS consist of and what is its role?
Cranial nerves and spinal nerves. Mainly sensory and motor neurons.
What is are afferent neurons?
Towards the CNS
What are efferent neurons?
Away from the CNS
What is the nerve structure in the PNS?
Axons. Blood vessels. Connective tissue.
Where are the sensory neurons located?
Cell bodies in ganglia close to CNS. They have synapses in spinal cord either directly to motor neurons or with interneurons.
Where are the motor neurons located?
Cell bodies are in the brain, spinal cord and ganglia.
How do sensory neuron and motor neurons meet at the spinal cord?
Sensory neurons in contact with spinal cord via the dorsal root. Motor neurons leave spinal cord via the ventral root. Dorsal and ventral root join to form nerve which contains both.
What is the PNS split into?
Somatic Nervous System and the Autonomic Nervous System.
What does the Somatic Nervous system consist of?
- Voluntary, under conscious control
- Sensory neurons (external stimuli)
- Motor neurons (activate skeletal muscle)
- Reflex loops
What does the Autonomic Nervous System consist of?
- Involuntary
- Inner workings
- Smooth and Cardiac muscle
- Glands
What are the features of a reflex loop?
Rapid. Automatic. Predictable response.
Describe the stages of the knee jerk reflex.
- Hit the patellar tendon
- Stretching of extensory muscle
- Sensory neurons sense stretch
- Transmit signal to motor neuron
- Contracts
- Inhibits the flexor muscle (reciprocal inhibition)
- Used in running and jumping
What is the Autonomic nervous System split into?
Sympathetic and Parasympathetic
What is the Parasympathetic NS?
Decreases heart rate. ‘Rest and digest’. Stimulates digestion and metabolic processes. Nerves originate from the brain, lower down spinal cord and the brain stem, Ganglia close or inside target organs.
What is the Sympathetic NS?
Increases heart rate and frequency of breathing. Mobilization of glucose. ‘Fight or Flight’. Active when a person is active. Some organs inhibited. Nerves originate from the middle part of the spinal cord. Ganglia form chain close to the spinal cord.
What is a reflex circuit (ANS)?
- Receptors, sensory neurons, go through 2 sets of motor neurons
- To get short reflex loops sensory transfers to second set of motor neurons
- In smooth, cardiac and glands
Describe the features of the spinal cord.
- Inner = grey matter
- Sensory endings, interneurons, cell bodies of motor neurons
- Dorsal and ventral regions
- Outer = white matter (nerve fibres)
Where are the cell bodies of somatic motor neurons?
Ventral side
Where are the cell bodies of autonomic motor neurons?
Just about ventral side
Where are the receiving somatic interneurons?
Just below the dorsal region
Where are the receiving autonomic interneurons?
Dorsal region
What are the different tracts in the white matter of the spinal cords?
Ascending and descending. Run between brain and spinal cord
What are the 3 main regions of the brain?
- Forebrain (complex cognitive function)
- Midbrain (basic function)
- Hindbrain (basic function)
What is meant by grey matter in the brain?
Close to surface - neuron cell bodies
What is meant by white matter in the brain?
Neuron axons, myelination, fatty
What is important in the organisation of the brain?
Sensory information arrives adjacent to the motor regions
What are the importance of glial cells in the CNS?
- More glial cells than neurons
- Structural and metabolic support for neurons
- Most common = astrocyte
- Form the blood-brain barrier
What is sensory transduction?
When stimuli is converted to electrical impulses
What are some examples of how a stimulus can create an action potential?
Change in temp or pressure can lead to a bend or a shape change of the membrane which opens ion channels
What are some examples of sensory receptors?
Chemoreceptors. Mechanoreceptors. Thermoreceptors. Photoreceptor.
What are simple receptors?
Free nerve endings
What are complex receptors?
Nerve endings surrounded by capsule of connective tissue
What are special sense receptors?
Specialized receptor cell. Don’t generate action potentials. Depolarization leads to release of neurotransmitters.
What is the All or Nothing Principle?
Size of stimulus doesn’t mean a different sized action potential as long as the threshold value is reached
What is stimulus strength determined by?
Firing rate
What does a high firing rate mean?
Strong depolarization - quickly reach the threshold
What does a low firing rate mean?
Depolarization would take longer
What is the firing rate determined by?
Number of sensory receptors active. Stronger = more sensory receptors activated
How is the stimulus location and type determined?
Each receptor can only respond to a specific stimuli and is always transported to a specific and the same region to the brain
What does localisation of the stimulus depend on?
Receptive field characterstics
What happens if there is a smaller receptive field?
More precise signal localisation
How can receptive field increase precision?
Overlap
Describe lateral inhibition.
- Increase the contrast between signals received from the centre and periphery of the stimulus
- Inhibitory interneurons
- Generates IPSPs
- Inhibits signal transmission by neighboring sensory receptors
- Strong stimuli send inhibition and increases contrast
How does human sense of smell work?
- Sensory endings on elfactory epithelium
- Chemoreception
- At first strong, then weakens
How does desensitization work?
Olfactory adaptation, high cytoplasmic Ca2+ leads to inhibition of cation channels inhibitory effect
How does human sensing of sound work?
- Sound waves, cochlea
- Pressure wave - basilar membrane bends upwards, cilia hairs bend
- K+ ions move into cell, depolarisation
- Ca2+ enter leading to fusion of vesicles with plasma membrane
