Pre-Midterm Content Conferences (1-4) Flashcards
How is the Nervous System organized?
1) Central Nervous System
-> Brain
-> Spinal Cord
2) Peripheral Nervous System
-> Somatic
-> Autonomic
Neurotransmitters can be
Inhibitor or Excitatory
Neurons
- cells of nervous system.
- able to transmit nerve impulses.
Glia
- cells of nervous system.
- able to transmit nerve impulses.
synapses
- space between pre- and post-synaptic terminals of two neurons, site of transmission
Neurotransmitters
- a chemical compound released by neurons that act on postsynaptic neurons
Neuron Vocabulary
1) Dendrite: primary target for synaptic input
2) Axon: signal transduction from cell body; reads out information
3) Action potential: electrical event that carries signal
4) Pre-synaptic terminal: where molecules are secreted into synaptic cleft
5) Post-synaptic specialization: contains receptors where molecules bind
6) Synaptic cleft: space between pre- and post synaptic terminals
Neurons
- specialized cells because they complete a single function: to transmit information across the nervous system via electrical impulses.
- sensory: afferent receptor.
- interneurons: transfer signals between sensory and motor.
- Motor: efferent effector.
Lobes and functions of the brain
1) Frontal: motor and high-level cognitive skills.
2) Parietal: sensory integration; association cortex.
3) Temporal: Auditory.
4) Occipital: Visual.
The brain - Ventricular System
- brain floats in bath of cerebrospinal fluid -> this fluid also fills large open structures, called ventricles, which lie deep in brain.
- the fluid filled ventricles keep brain buoyant & cushioned.
- there are 4 ventricles: 2 lateral (1 in each cerebral hemisphere), third ventricle in the diecephalon, and 4th ventricle in the hindbrain.
The brain: Glymphatic System
- cooperation of glial cells and lymph velles (lymphatic system) to transport and accumulate waste out of the brain.
- clean CSF replaces the ventricular spaces.
Anatomy of the Spinal Cord
1) External Anatomy:
-> Anterior median fissure
-> Posterior Median Sulcus
2) Internal Anatomy:
- Grey matter (nerve cells bodies - located in center of Spinal Cord)
- White matter (surround grey matter, composed of myelinated axons)
- Central canal: small channel with CSF in center of spinal cord, controls with the ventricular system in the brain.
- Dorsal (posterior) horns: sensory neurons, in the back of spinal cord.
- Ventral (anterior horns): motor neurons, in the front of spinal cord.
- Lateral horns: in thoracic and lumbar segments of spinal cord, contains sympathetic neurons.
- Dorsal root ganglia: cells bodies of sensory neurons, in dorsal roots of the spinal nerves.
- Dorsal root: sensory fibres, enters the spinal cord.
- Ventral root: motor fibers, exits the spinal cord.
3) Meninges:
- Dura mater: tough outermost layer surrounding spinal cord.
- Arachnoid matter: middle layer, located between dura mater and pia mater.
- Pia matter: innermost layer that adheres to surface of spinal cord.
What are ways to study neural circuts?
- Electrophysiological Recordings
- Calcium Imaging
- Optogenetics
What are ways to study neural circuits?
- Genetic Analysis
- Structural Imaging
- Non-invasive functional imaging (EEG, CT, TMS, fMRI)
Somatic Sensory System
- Cutaneous Touch
- Proprioception
- Pain, Temperature & Sensual touch
Cutaneous Touch
- Mechanical perturbations lead to depolarization of afferent.
- Different types of encapsulations detect different features of touch:
1) Small Receptive Field;
- Merkel (shape and texture perception, edges, points, corners, curvature)
- Meissner (motion detection, grip control, skin motion)
2) Long Receptive Field;
- Pacinian (perception of distant events through transmitted vibrations - tool use)
- Ruffini (Tangential force: hand shape, motion direction, skin stretch)
Proprioception
- Sense of Self
- Sensory afferents coil around intrafusal muscle fibres, which detect the rate of change of muscle length.
Proprioception: Muscle Spindles
1) Primary endings - Group Ia
- rapidly adapting
- dynamic limb movement
- mono and polysynaptic excitatory alpha motor neurons
2) Secondary Endings - Group II
- slow adapting
-awareness of static positions
- sustained response to stretch
- polysynaptic excitatory alpha motor connections
3) y-motor neurons
- change intrafusal fibre tension
- increases afferent sensitivity to stretch
- dynamic gamma motor neurons and static gamma motor neurons.
-> Tension from muscle stretching opens ion channels. Increases stretching produces increased firing via their mechanically-gated ion channels.
Golgi Tendon Organ
- mechanoreceptor involved in proprioception. Plays a role in less conscious muscle activity - such as reflexes.
Are the somatic motor neurons dorsal or ventral to the somatic sensory interneurons?
1) Somatic Motor Neurons:
- located in the ventral (anterior) horn of the gray matter.
- Control skeletal muscles.
- Efferent neurons (carry signals form the CNS to effectors)
2) Somatic sensory interneurons:
- located in the dorsal (posterior) horn of the gray matter.
- process sensory information from the body.
- afferent neurons (carry signals from sensory organs to the central nervous system)
-> positioning due to layout of the spinal cord, with sensory neurons entering the dorsal root and motor neurons exiting via the ventral root.
What are the characteristics of the different order neurons?
1) First-order neuron:
- primary sensory neuron
- body: ipsilateral dorsal root ganglion
- face: trimegemial ganglion
2) Second-order neuron:
- brainstem relay station
- body: ipsilateral gracile/cuneate nuclei
- face: trigeminal nucleus
3) Third-order neuron:
- thalamic relay station
- body; contralateral (lateral) nuclei in thalamus
- face: contralateral (medial) nuclei in the thalamus
What are the roles of the different order neurons in “cutaneous touch”?
1) First order:
- brings in sensory information from ipsilateral side
2) Second order:
- sends information (axons) to contralateral side (decussation)
3) Third order:
- Sends information to cortex
Pathway in proprioception
1) Lower body Proprioception:
- follows dorsal spinocerebellar tract via Clarke’s nucleus.
- First-order neurons synapse in Clarke’s nucleus.
- Second-order neurons ascend to the ipsilateral cerebellum.
2) Upper Body Proprioception:
- Similar to tactile pathway, involving external cuneate nucleus.
- First order neurons synapse in the external cuneate nucleus.
- Second-order neurons convey the information to the ipsilateral cerebellum.
3) General:
- synapse onto the ipsilateral cerebellum - involved in unconscious proprioception.
Somatotopic Representation
- The representation of body parts and
the various types of sensations are
highly organized in the thalamus and
the cortex! - The organization of the somatosensory cortex has no relationship to the actual
proportions of our body.
What is sound?
- displacement of air molecules - pressure waves generated by vibrating air molecules.
- waveform = its amplitude plotted against time.
- simplest type of sound is a pure tone (e.g. tuning fork). or a single sine wave (pure tones are NOT common in real life).
What are the properties of sound?
- amplitude = dB
- frequency = Hz
- Waveform (amplitude across time)
- Phase - every cycle of the soundwave. The exact point in time for which the sound is being perceived. Important for localizing where sound comes from.
Complex Sounds
- sounds like speech, music, and environmental stimuli contain energy, distributed across a broad frequency spectrum.
- examples of different natural sounds.
- animal vocalizations, speech and music contain highly periodic (tonal and harmonic) elements, whereas environmental sounds such as wind lack periodic structure.
The audible spectrum
- different species emphasize the frequency of their own vocalizations
- for humans, 20hz to 20kHz
- as we get older, stop stop being able to hear the higher frequency
- max 15-17 Hz as an adult
The auditory system
- there is mechnoelectrical transduction of sound (air vibrations) into neural activity.
Auditory Function
- Auditory system transform sound (air vibration patterns) into neural activity (mechanoelectric transduction)
1) External and middle ears collect and amplify sound waves and transmit to the fluid filled cochlea of inner ear.
2) In the inner ear, hair cells transduce frequency, amplitude, and phase of the signal into electrical signals.
3) Acoustical decomposition results in systemic representation of sound frequency along the length of the cochlea (tonotopy).
External Ear
- Pinna, Concha, Auditory Meatus
- Boosts and filters sound input
- Provides clues on the elevation or amplitude of the sound (is the sound coming from up or down)
- The auditory meatus boosts and concentrates sounds at frequencies around 3khz and focuses this sound energy onto the tympanic membrane.
Middle Ear
- transition of sound from air to water through bones (malleus, incus, stapes)
- amplification: pressure of the sound get kind of boosted from the tympanic membrane to the ear by 200x
What is the efficiency of sound transmission in the inner ear regulated by?
- tensor tympani
- stapedius muscles
- when paralyzed = hyperacusis
The inner ear
- the cochlea transforms sonically generated pressure waves into neural impulses carried by the auditory nerve (sensory transduction) to the cortex
- also acts as a mechanical frequency analyzer - decomposing acoustical waveforms into their elements - tonotopy
The cochlea
- fluid filled (perilymph/endolymph) tube with specialized hair cells
- sound waves (in scala media fluid) cause the basilar membrane to vibrate.
- vibrations cause hair cells to press against tectorial membrane and produce action potentials.
The Cochlea: Basilar Membrane
- differentially sensitive to different frequencies (varying stiffness)
- base -> high frequencies
- apex -> low frequencies
this is called TONOTOPY - a complex sound will displace membrane in several regions
Transduction: Hair Cells
Hair cells
- sensory neurons
- between the basilar membrane and tectorial membranes
- inner hair cells: transduction
- outer hair cells: efferent innervation
-> cochlear amplifier
-> otoacoustic emissions
Hair cells and the mechanotransudction of sound waves
- B-tip links that connect adjacent stereocilia are believed to be mechanical linkages that open and close transduction channels
- inner hair cells are the sensory receptors
- each hair bundle contains from 30 to a few hundred stereocilia - they are graded in height and arranged in a bilaterally symmetrical fashion.
- fine filamentouts structures - tip links, connect the tops of adjacent stereocilia and translate hair bundle movement into a receptor potential
Physiology of Inner Ear
- Endocochlear Potential (potential difference between endolymph and perilymph, essential for hair cell function and signal transmission).
- Endolymph:
Stereocilia of hair cells
Rich in K+, poor in Na+ - Perilymph:
- Basal surface of hair cells
- Poor in K+, rich in Na+
What is the process of transduction of hair cells?
- inner hair cells have cilia that have tip links. cilia are displaced.
- tip links mechanically pull open K+ channels.
- hair cells depolarize:
Ca2+ influx
Neurotransmitter release onto auditory nerve. - movement in the opposite direction compresses the tip-links, closes the channels and hyper polarizes the cell.
- because some channels are open at rest, the receptor potential is biphasic.
Transduction of sound waves
- movement of the stereocilia back & forth modulates ionic flow to produce a graded receptor potential.
- transmitter release triggers action potential in CN VIII following the up and down vibration of the basilar membrane.
- Hair cell transduction is fast & sensitive - 10 microseconds - essential for sound localization.
- Mechanical gating of ion channels is essential for this rapid, high resolution signal.
- Damage to stereocilia (by high intensity sounds) leads to irreversible hearing loss.
- damage to tip-links leads to temporary hearing loss as tip links can regenerate within hours.
