Biology - Chapter 11.4: Nervous System Flashcards
Axon hillock
- Area where the axon is connected to the cell body
- Responsible for summation of graded potentials
Myelin sheath
- Fatty insulation of the axon that speeds up action potential propagation by stopping ion exchange
- CNS: oligodendrocytes
- PNS: Schwann cells
Nodes of ranvier
- Gaps between myelin sheath where ion exchange occurs
- Propagation of action potential occurs here
Saltatory conduction
Propagation of action potential along myelinated axons from one node of Ranvier to the next node
Steps of an Action Potential
1) At resting potential, membrane potential is around -70 mV and is maintained by Na+/K+ ATPases (3 Na+ ions out, 2 K+ ions in). K+ leak channels also maintain resting potential.
2) Stimulus causes threshold potential reached (-55mV), voltage-gated Na+ channels open, resulting in depolarization = action potential.
3) Repolarization occurs as voltage-gated K+ channels open, letting K+ out. Membrane potential becomes negative again.
4) Hyperpolarization occurs as the membrane potential becomes even more negative than normal resting potential. Results in a refractory period = no action potential can be fired.
5) Membrane potential returns to normal resting potential through the pumping of Na+/K+ ATPases and K+ leak channels
Absolute refractory period
- No other action potential can be fired, no matter how powerful
- Due to the inactivation of voltage-gated Na+ channels after they open
Relative refractory period
-A stronger stimulus could cause another action potential to fire
Steps of Synaptic Transmission
1) Action potential reaches presynaptic axon knob, opening voltage-gated calcium channels and releasing Ca2+ ions into neuron
2) Ca2+ ions cause synaptic vesicles to fuse and undergo exocytosis: releasing neurotransmitters into synapse
3) Neurotransmitters bind to ligand-gated ion channels, producing a graded potential
4) Graded potentials summate at the axon hillock and a potential action potential is fired if threshold potential is reached.
EPSP
- Excitatory postsynaptic potential
- graded potential that depolarizes membrane
- Na+ ion gates to open and let Na+ ions flow into the cell
IPSP
- Inhibitory postsynaptic potential
- graded potential that hyperpolarizes the membrane
- K+ ion gates open and let K+ ions flow out of cell
Microglial cells
Macrophages that protect the CNS
Macroglial cells
- Astrocytes
- Schwann cells (PNS)
- Oligendrocytes (CNS)
- Satellite cells
- Ependymal cells
Astrocytes
- Form the blood-brain-barrier
- help recycle neurotransmitters
- provide blood supply to CNS
Satellite cells
- help recycle neurotransmitters
- provide blood supply to PNS
Ependymal cells
-secrete cerebrospinal fluid which cushions the CNS
Frontal lobe
- Higher function processes such as decision making, problem solving, judgement, planning ahead, consequences
- Works with limbic system for memories and emotions
- Attention/concentration
Temporal lobe
- Speech/language
- Hearing
Occipital lobe
-Vision
Parietal lobe
- Spatial/visual perception
- Touch/pain/temperature sensation and integration
Cerebellum
Responsible for coordination of movement
Brainstem
- Midbrain (relays senses)
- Pons (relays messages from cerebellum to forebrain)
- Medulla oblongata (heart/breathing rate, blood pressure, toxin sensing)
Thalamus
Relay center
Limbic system
-emotion/memory/learning/motivation
- Hypothalamus
- Hippocampus
- Amygdala
Sensory (afferent) neurons
-Send signals to the spinal cord and the brain via dorsal roots
Motor (efferent) neurons
-Send signals back out to the muscles through ventral roots
Meninges
-Protects the brain, has 3 layers (outermost –> innermost):
Dura mater–> arachnoid –> pia mater
Peripheral Nervous System Division
- Somatic (voluntary motor action and sensory input)
- Autonomic (involuntary)
Nociceptors
pain receptors
Autonomic Nervous System Division
- Sympathetic (fight or flight)
- Parasympathetic (rest and digest)
Sympathetic Nervous System
- Releases sugar into body for energy
- Increases heart rate for oxygen delivery
- Dilation of lungs and pupil
Parasympathetic Nervous System
- Relaxation of muscles
- Decrease in heart rate
- Maintenance of homeostasis
- Increase in gastrointestinal activity
Sympathetic Nervous system Pre/Postganglionic
- short preganglionic nerves and long postganglionic nerves
- uses acetylcholine for preganglionic
- uses noradrenaline/adrenaline for postganglionic
Parasympathetic Nervous system Pre/Postganglionic
- long preganglionic nerves and short postganglionic nerves
- uses acetylcholine for both
Outer Ear
-Takes in sound waves and the tympanic membrane transfers the sound from outer ear to middle ear
Middle Ear
- Composed of three bony ossicles –> malleus, incus & stapes
- Ossicles transfer vibrations through the middle ear and amplify the signal
- Stapes transfers vibrations from middle ear to inner ear via the oval window
Cochlea
Uses fluid and hairs to convert mechanical signal into a neuronal signal, known as transduction
Round window
Membrane covered opening between middle ear and the inner ear, helps fluid expand and vibrate
Semicircular canals
Fluid and hairs just like cochlea, gives information about the person’s movement and balance
Cornea
- Transparent
- Focuses light and protects the eye
Iris
-Controls the size of the pupil
Pupil
-Controls how much light enters
Lens
-Focuses images on retina
Retina
-Back of the eye that has photoreceptors (rods and cones)
Fovea
-Highest concentration of photoreceptors in the retina and responsible for high acuity vision
Amacrine and bipolar cells
Take information from rods and cones, transmitting the information to ganglion cells of the optic nerve fibers
Optic nerve
Bundle of axons that transmit visual information to the brain
Optic disk
Blind spot of the eye, where the optic nerve passes through to reach the brain
Sclera
Protective connective tissue that surrounds the eye, the white part of the eye
Choroid
Vascular connective tissue
