Chapter 3 - NEURONS COMMUNICATE QUICKLY Flashcards
What is the nervous system
Coordinates our voluntary and involuntary actions by receiving and processing information from sense organs
What are neurons
The basic structural and functional units of the nervous system. Highly specialised cells
name all the parts of a neuron
- Dendrites
- Cell body
- Nucleus
- Axon
- Myelin sheath
- Neurilemma
- Schwann cell
- Node of ranvier
- axon terminals
what is the cell body
Part of the neuron that contains the nucleus and is responsible for the functioning of the cell
what are the dendrites
An extension of the cell body of the nerve cell. Carries nerve impulses into the cell body
what is the axon
An extension of the cell body of the nerve cell. Carries nerve impulses away from the cell body. Divides into branches called the axon terminals (output)
What is the myelin sheath
A white fatty sheath that surrounds some nerve fibres.
what is the neurilemma
Outermost coil of Schwann cell. Helps repair in injured fibres
what are the three functions of the myelin sheath
- Acts as an insulator (stops interference + signal becoming weak)
- Protects axon
- Speeds up the movement of nerve impulses
What is the node of ranvier
A gap in the myelin sheath, helps speed up movement of nerve impulses
What are myelinated fibres
Nerve fibre that has myelin sheath. Appears white (white matter)
What are unmyelinated fibres
Nerve fibre that has no myelin sheath. Appears grey (grey matter)
What are Schwann cells
Cell that wraps around a nerve fibre. Outside of the brain and spinal cord it forms the myelin
How is Myelin formed in the brain and spinal cord
Produced by oligodendrocytes
What is a synapse
The junction between the branches of adjacent neurons
what are neurotransmitters
Molecules that carry a nerve impulse across a synapse as the neurons don’t actually touch
What is a neuromuscular junction
The junction between nerve cell and skeletal muscle cell
What are the two ways neurons can be classified
Based on their function or structure
What are the three functional types of neurons
- Sensory (afferent) carry messages from sense organs to CNS
- Motor (efferent) carry messages from CNS to the effectors (muscles/glands)
- Interneurons are the link between sensory and moto neurons
What are all the names of a interneuron
Association, Connector, Relay neuron
what are the four structural types of neurons
- Multipolar, have 1 axon and multiple dendrites (eg interneurons)
- Bipolar, 1 axon and 1 dendrite on opposite sides of cell body (eyes, ears, nose)
- Unipolar, just have one extension, an axon (found in insects)
- Pseudouniploar, have properties of bother unipolar and bipolar neurons. Single axon from cell body
What are nerve fibres
any long extension of cytoplasm of a nerve cell body, refers to an axon
what is a nerve
bundles of nerve fibres held together by connective tissue
what is a nerve impulse
the electrochemical change that travels along the membrane of a nerve cell.
why is a nerve impulse described as electrochemical change
Because it involves a change in electrical voltage that is brought about by changes in the concentration of ions inside and outside the cell membrane
like charges
repel (+ and +, - and -)
opposite charges
attract (+ and -)
what is potential difference
a difference in electrical charge between two locations
membrane potential
- electrical voltage across membrane of cell
- Extracellular fluid contains a high concentration of sodium chloride so most of its charged particles are positive sodium ions and negative chloride ions
- Intracellular fluid has low concentration of sodium and chloride ions. The main positive ions are potassium and the negative ions come from a variety of organic substances made by the cell
Resting membrane potential
Membrane potential of unstimulated nerve cells (-70mV)
Leakage channels
protein channel that is always open
Voltage gated channel
protein channel that is opened by electrical stimulus
polarised
inside of the membrane of a nerve cell has a negative electrical charge compared with the outside
action potential
the rapid depolarisation and repolarisation of the cell membrane
what are the three parts of action potential
- Depolarisation
- Repolarisation
- Refractory period
what is depolarisation
- The sudden increase in membrane potential, occurs if level of stimulation exceeds 15mV (threshold).
- More sodium ions move into the cell, making the intracellular fluid less negative, increasing the potential difference
- If stimulus is strong enough to increase the potential pass the threshold (-55mV) then all or none response is triggered
- membrane becomes depolarised
all or none response
Response of constant size regardless of strength of stimulus. Nerve impulse is transmitted at full strength or not at all
depolarised
No difference in electrical charge between the inside and outside of the membrane
what is repolarisation
- Process of becoming repolarised (returned to polarised state)
- Sodium channels close, stopping influx of sodium ions
- Voltage gated potassium channels open, increasing flow of potassium out of cell
- inside of membrane becomes more negative than outside, decreasing membrane potential
- Potassium channels remain open longer than needed causing hyperpolarisation
what is hyperpolarisation
membrane of nerve cell when it has lower membrane potential than normal
what is the refractory period
once sodium channels have opened they become inactivated, meaning they are unresponsive to stimulus Therefore cannot undergo another action potential for a brief period. lasts from -55mV to -70mV
explain conduction along an unmyelinated fibre
- Depolarisation of one area of the membrane causes a movement of sodium ions into the adjacent areas. This movement stimulates the opening of the voltage gated sodium channels in the next part of the membrane, which initiates an action potential in that area
- Back flow prevented by refractory period
- Although rare, if stimulus occurs in middle of a fibre impulses will travel in both directions
Explain conduction along myelinated fibres
- Where the nerve fibre is surrounded by myelin, ions cannot flow between inside and outside of the membrane and an action potential cannot form
- Instead action potential jumps from one node of ranvier to the next (saltatory conduction)
- Allows for faster travel
How are we able to determine the strength of a stimulus
- Strong stimulus causes depolarisation of more nerve fibres than a weak stimulus
- Strong stimulus produces more nerve impulses in a given time than a weak stimulus
what is the process of transmission across a synapse
- When the nerve impulse reaches the axon terminal, voltage gated calcium ion channels are activated
- as there is a higher concentration of calcium ions in the extracellular fluid, they flow into the cell at the presynaptic axon terminal
- Causes synaptic vesicles to fuse with the membrane, releasing special chemicals called neurotransmitters by exocytosis
- Neurotransmitters diffuse across synapse and attach to receptors on the membrane of the next neuron
- This stimulates ligand gated protein channels to open which allows the influx of sodium ions and initiates an action potential in the post synaptic membrane
How are neurotransmitters removed from the synapse
- Reabsorption by presynaptic membrane
- Degraded by enzymes
- Moving away through diffusion
how do chemicals effect the transmission of nerve impulses
Stimulants such as caffeine stimulate transmission at the synapse. Drugs like anaesthetics or hypnotics depress the transmission. Venom can affect the neuromuscular junction
what are the five types of receptors
Thermoreceptors, Osmoreceptors, Chemoreceptors, Mechanoreceptors (touch) and nociceptors (pain)
Thermoreceptors
Temperature receptor located in the skin or the hypothalamus
Osmoreceptors
Receptor sensitive to osmotic pressure of body fluids located in hypothalamus
Chemoreceptors
Receptor sensitive to particular chemicals. Nose, mouth internal organs (blood vessels)
Mechanoreceptors
receptor sensitive to touch. Skin
nociceptors
Receptor stimulated by damage to tissues. Skin, mucous membranes, most organs
what is a spinal reflex
Reflex carried out by the spinal cord without involvement from the brain
what is a reflex arc
the pathway travelled by nerve impulses from receptor to effector in a reflex
innate reflexes
reflexes that are determined genetically. eg suckling, chewing, grabbing
acquired reflexes
response to a stimulus that is learnt through practice. Eg, balance, slamming on brakes, catching a ball
What are the four differences between the actions of nerves and hormones
- Nervous responses are more rapid than hormonal as nerve impulses travel rapidly along nerve fibres while hormones are transported in the bloodstream
- Nerve impulses bring about an immediate response which lasts for a short time. Hormones are slower acting but can last a considerable time
- Nervous messages are an electrochemical change that travels along membrane of neuron. Endocrine messages are hormones that are transported by blood
- Nervous impulses travel along a nerve fibre to a specific part of the body and often influence just one effector. Hormones travel to all parts of the body and effect a number of different organs
What are three similarities between the actions of nerves and hormones
- some substances function as both hormones and neurotransmitters. (Noradrenaline, antidiuretic hormone)
- Hormones such as oxytocin and adrenaline are secreted by neurons into the extracellular fluid
- Some hormones and neurotransmitters have the same effect on the same target cells (noradrenaline, glucose)
