Nervous system (neurons communicate quickly) Flashcards
What are the functional types of neurons
- Sensory/Afferent/Receptor – carry impulses from receptors in skin or sense organs to the CNS
- Motor/Efferent/Effector – carry impulses from the CNS to the effectors (muscles and glands)
- Interneurons/Connector/Relay/Association –located in the CNS providing a link between sensory and motor neurons
Structural types of neutrons
- Unipolar
ONE AXON
Not in humans - Bipolar
ONE AXON
ONE DENDRITE
Eye, ear, nose - Pseudounipolar
ONE AXON THAT SEPARATES
One to dendrites, one to axon terminals
Sensory - Multipolar
ONE AXON
MULTIPLE DENDRITES
Interneurons, motor
Nerve Impulses
- Travels along a nerve fibre as an electrochemical change
- Extracellular fluid is more positive due to Na+ and Cl-. The potential difference between the two places can be measured – voltage, measured in mV
- Intracellular fluid is more negative due
organic molecules (eg proteins) - This results in a resting membrane potential
of -70mV in nerve cells (the potential
inside is 70mV less than the outside)
What happens during DEPOLARISATION
- Sudden increase in membrane potential (+15mV)
- Stimulation causes ligand channels to open, allowing Na+ into the cell
- If stimulus is strong enough to reach -55mV threshold, voltage gated channels will open
- Na+ flood into the cell, up to +40mV
- All or nothing response
What happens during REPOLARISATION
- Sodium channels close
- Voltage-gated K+ channels open increasing flow of K+ out of the cell
- Inside becomes more negative than outside
- K+ channels remain open = membrane potential drops below -70mV = HYPERPOLARISATION
- Sodium-potassium pump will move 3x Na+ out and 2x K+ into the cell to re-stablish correct concentrations
What happens during REFRACTORY PERIOD
- Na+ channels become inactivated after opening
= for a short time, membrane cannot be restimulated
= action potential travels in one direction - Lasts -55mV until return to -70mV
What is synapses
- The junction between two neurons
- Allows impulses to travel from the axon terminal of one neuron to the dendrites of another
- Neurons don’t physically touch – synapses are gaps
- Neurotransmitters are chemicals used to carry the impulse across the synapse
- A neuromuscular junction is found where an axon meets a skeletal muscle
Describe the steps of synapses
- Impulse reaches the axon terminal and activates voltage-gated calcium channels
- Calcium ions flow into the pre-synaptic axon terminal (due to higher concentration in the extracellular fluid)
- This causes synaptic vesicles to fuse with the membrane and release neurotransmitters by exocytosis
- Neurotransmitters diffuse across the synapse and attach to receptors on adjacent neuron
- This causes ligand-gated channels to open, allowing sodium ions to flood in, initiating an action potential in the post-synaptic neuron
Neurotransmitters
Removed from synapse:
1. Being reabsorbed by presynaptic membrane
2. Degraded by enzymes
3. Moving away from synapse by diffusion
- Stimulants (eg coffee) stimulate impulse transmission
- Hypnotic drugs and venom depress impulse transmission
- Nerve agents (nerve gases) cause a build up of acetylcholine causing all muscles to contract – loss of muscle control – prevents breathing
Impulse Tranmission
- Unmyelinated fibres:
Without myelin insulating the axon, impulses must travel the entire length of the axon
Slower conduction - Myelinated fibres:
Conduction can only occur where the axon is exposed (nodes of Ranvier)
Impulse will “jump” between nodes of Ranvier
Saltatory conduction
Faster
Size of Impulses
As long as the threshold is reached (-55mV) an action potential will be generated
- All action potentials are the same “size” – “all or nothing” response
How do we distinguish different stimuli intensities?
- A “strong” stimulus will cause MORE fibres to be activated
- A “strong” stimulus will cause action potentials for a LONGER period of time
What are the different types of receptors?
- Thermoreceptors – heat and cold in skin and hypothalamus
- Osmoreceptors – concentration of substances dissolved in water of blood plasma; higher concentration = higher osmotic pressure; in hypothalamus
- Chemoreceptors – stimulated by certain chemicals in nose, mouth and internal organs
- Touch – mostly in the skin; stimulated by pressure and vibrations
- Pain (nociceptors) – stimulated by damage to tissue (eg cut, bump, poor blood flow, heat, chemicals) in most organs except brain
Reflexes
- A rapid, automatic response to a stimulus.
- They ALL have 4 properties:
1. Require a stimulus
2. Involuntary
3. Rapid
4. Stereotyped (occurs the same way every time) - Some are coordinated by the brain; most come from spinal cord
- WHY?
To keep us alive and safe from danger
What are different types of reflexes?
Spinal reflex arc- Conscious realisation occurs AFTER the response has occurred – takes longer for impulses to travel to the brain for processing.
INNATE – present from birth.
Eg salivation, ejaculation, blushing, pupils dilating, babies suckling.
AQUIRED – learnt behaviours
Eg maintaining balance when riding a bike, slamming on brakes when driving, catching a ball
Cell Body
- Part of neuronal that contains the nucleus
- Responsible for controlling the functioning of the cell
