CNS S1 Flashcards
CNS
Brain and spinal cord
PNS
Made up of neurons and parts of neurons outside of CNS. Somatic and autonomic nervous system
Somatic nervous system
Controls voluntary action via skeletal muscle
Autonomic nervous system
Visceral functions such as heart rate, breathing, digestion (enteric nervous system)
How many nervous are in the CNS/PNS
86 billion in brain, 1 billion in spinal cord. 100-600 million in PNS
CNS and CSF route
3rd ventricle between lateral ventricles > 4th ventricle > central canal
Grey matter
Nerve cell bodies, unmyelinated axons and dendrites
Cell body organization
Organized in clusters called nuclei
White matter
Myelinated axons running in bundles called tracts
PNS neuron clusters and axons nomenclature
Clusters of neurons are ganglia and bundles of axons are nerves
How many neurons are fired at any moment?
4%, only one AP fires every 6s in the cortex
Spinal cord
31 segments, each with a pair of spinal nerves
Dorsal root
Carries afferent (incoming sensory) signals
Ventral root
Carries efferent (outgoing) motor signals from CNS to body
Grey matter in the spinal cord
Mainly in the middle and consists of a dorsal and ventral horn. Have motor and sensory nuclei
Dorsal horn
Contain sensory nuclei. Somatic nuclei get signals from skin, visceral nuclei get signals from internal organs
Ventral horn
Efferent nuclei. Autonomic send commands to glands and smooth muscle, somatic to skeletal muscle
White matter in spinal cord + tract components (3)
Consist of tracts
1) ascending tracts: sensory signals to brain (dorsal)
2) descending tracts: signals from brain (ventral)
3) propriospinal: stay in spinal cord
Brain stem
Medulla, pons and midbrain Control centre for many autonomic functions and reflexes.
Cranial nerves
Nerves that enter or leave the brain. 3-10 and 12 are in brain stem
Diencephalon
Made up of thalamus, hypothalamus, pituitary and pineal gland
Thalamus and hypothalamus
Thalamus: processes information to and from cerebral cortex
Hypothalamus: regulates behaviour and endocrine/autonomic homeostasis
Cerebrum
2 hemispheres connected by the corpus callosum
Cerebral grey matter
Cortex, limbic system (motivation and memory) and basal ganglia (movement)
Left and right hemisphere functions
left: speech, writing, language, math
right: analysis by touch, spatial analysis
Limbic system
Cingulate gyrus, amygdala, hippocampus
Senses
9 senses. 5 special and 4 somatic
Special senses
Vision, hearing, equilibrium, taste, smell. Have a sense organ that isn’t skin
Somatic senses
Touch, temperature, proprioception and nociception (pain and itch)
Transduction
The process of converting stimuli into electrical signals
Chemoreceptors
Respond to specific molecules or ions
Mechanoreceptors
Respond to mechanical energy such as pressure, vibration, gravity, sound
Photoreceptors
Respond to light
Thermoreceptors
Temperature
Perceptual threshold
The weakest stimulus that will cause conscious perception in the organism
Labelled lines modality
The modality is revealed by which axons carry the signal
Population coding of intensity
Represents stimulus intensity by the number of active neurons
Phasic cells
Respond briefly to any change and then cease firing. Ex, retinal cells
Tonic cells
Maintain activity when the stimulus isn’t changing
Phasic-tonic
React to change but don’t return all the way to zero firing when stimulus is constant
Temporal changes
Changes through time, between one moment and the next
Spatial changes
Differences between neighbouring regions in space
Edges
Edges convey information between two different areas conveying different stimuli. Can be accentuated by lateral inhibition
Thalamus exception
Olfactory pathways are the only ones that don’t project through thalamus
Equilibrium pathways
Project mainly to the cerebellum
Lens
Transparent disk that focuses light and is suspended by ligaments called zonules
Anterior chamber
The front of the lens and is filled with aqueous humour
Vitreous chamber
Filled with a vitreous body which helps maintain eye shape
Cornea
Transparent bulge at the front of the eye that is continuous with the sclera. Lights enter through cornea
Pupil
A hole in the iris that changes in response to light. Controlled by the pupillary muscle
Refraction
Allows us to obtain a bright, infocus image. The bending of light.
Refractive index
Light bends when it enters a different medium. Air and collagen of the eye are different so light bends to make a right angle
Lens composition
Mesh of long cells without nuclei, packed by crystallin proteins
Convex lens
Fatter in the middle and thinner at edges. Makes light converge at a focal point
Concave lenses
Thinner in the middle and fatter at edges. Disperse light
Accommodation
The process of changing the lens to alter the amount of refraction. Round lens bends light more, closer focal point. Skinnier lens bends light less, further focal point
Focal point
Must fall on the retina. To bring a closer object into focus, the lens is rounder
Ciliary muscle
Ring-shaped. Parasympathetic nerves contract the ring, making lens rounder and sympathetic signals relax the muscle, making lens flatter
Presbyopia
Lens stiffening, hindering accommodation
Hyperopia
Far-sightedness caused by focal point falling behind retina. Convex lens fixes it
Myopia
Near-sightedness caused by a focal point in front of the retina. Solved by a concave lens
How many cones and rods are in the retina
6 million cones and 120 million rods
Structure of rods and cones
Outer segment: disk-like layers of membrane that contain visual pigment
Inner segment: contains nucleus and organelles
Basal layer: found in inner segment and contain synapse
Photoreceptor mechanism
Pigment molecules change shape when light hits, hyperpolarizing the cells and reducing glutamate
Pigment in rods and cones
Rhodopsin in rods, 3 other pigments in 3 types of cones
Photoreceptor distribtuion
Most densely packed in the macula found in the fovea
Cones vs rods
Cones are for bright light, rods are for dim. Cones are less sensitive and can distinguish colours
Cone and rod distribution
Cones are almost exclusively in the fovea, peripheral retina contains rods
Bipolar cells
Have center-surround receptive fields, with a round center region and.a hoop surround
On-center cells
Excited by light in the center of the field, inhibited by light in the surround
Off-center cells
Inhibited by light in the center and excited by light in the surround
Bipolar cell projection
Project onto retinal ganglion cells which have center-surround receptive fields
Magnocellular ganglion cells
Provide information used by the brain to infer movement of objects. Phasic
Parvocellular ganglion cells
Provide information used to infer form and fine detail
Melanopsin ganglion cells
Photoreceptors with their own visual pigment, melanopsin
Optic nerve
Cranial nerve II. When each nerve reaches the optic chiasm, half cross to the other side of the brain (nasal half)
Why do optic fibers cross
For information from the right hemifield to come together in the left cerebral hemisphere and vice versa
Optic tracts
Nerve bundles emerging from the chiasm and end in the 2 lateral geniculate nuclei in the thalamus
What wavelengths do humans see
400nm (violet) to 700nm (red) and powerful infrared light
Three types of cones
Red, green and blue
Blue cones
Peak at 420nm and prefer blue light
Rhodopsin
Peak at 498nm and prefers blue-green light. Doesn’t contribute to colour vision
Green cones
Peaks at 533nm and prefers yellow-green light
Red cones
Peak at 564m, and prefers yellow light
Spectral colours
Colours that can be evoked by a light of a single wavelength (rainbow colours)
Extraspectral colours
Can only be evoked by a mix of wavelength
R + G cells
Ganglion cells excited by red and green to make yellow
R - G cells
Ganglion cells excited by red and inhibited by green
B - R - G cells
Excited by blue and inhibited by red or green
Daltonism
Red-green colourblindness. Rarely occurs in women
Reflectance
A surfaces tendency to reflect a certain wavelength of light and absorb others. Doesn’t change
