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2.0 Human Anatomy and Physiology 1 Exam 3
General Senses
Receptors transduce different types of energy
1. Organization & Functions of the Nervous System
Divisions:
Central Nervous System (CNS): Brain and spinal cord; processes and integrates information.
Peripheral Nervous System (PNS): Nerves and ganglia outside the CNS.
Somatic Nervous System: Controls voluntary movements and sensory input.
Autonomic Nervous System: Regulates involuntary processes (e.g., heart rate, digestion).
Sympathetic: "Fight or flight" response.
Parasympathetic: "Rest and digest" response.
Functions:
Sensory input, integration of information, and motor output.
2. Glial Cells and Functions
Astrocytes: Maintain the blood-brain barrier, regulate ion balance, and provide structural support.
Oligodendrocytes (CNS) / Schwann Cells (PNS): Form myelin sheaths around axons for faster signal conduction.
Microglia: Act as immune cells of the CNS, removing debris and pathogens.
Ependymal Cells: Line ventricles and produce cerebrospinal fluid.
Satellite Cells (PNS): Surround neuronal cell bodies in ganglia, providing support and nutrients.
3. Neurons: Structure and Function
Structure:
Cell body (soma): Contains the nucleus and organelles.
Dendrites: Receive incoming signals.
Axon: Transmits electrical signals to target cells.
Axon terminals: Release neurotransmitters at synapses.
Function:
Specialized for signal transmission via electrical and chemical means.
4. Membrane Potentials
Resting Membrane Potential:
Typically ~ -70 mV.
Maintained by the Na⁺/K⁺ pump and ion channels.
Graded Potentials:
Localized changes in membrane potential.
Magnitude varies with stimulus strength.
Can be depolarizing (more positive) or hyperpolarizing (more negative).
Action Potentials:
All-or-none signals triggered when the membrane potential reaches a threshold (~ -55 mV).
Phases:
Depolarization: Na⁺ channels open, and Na⁺ enters the cell.
Repolarization: K⁺ channels open, and K⁺ exits the cell.
Hyperpolarization: Excess K⁺ efflux before returning to resting state.
5. Chemical Synapses and Neurotransmitters
Chemical Synapse:
Presynaptic neuron releases neurotransmitters into the synaptic cleft.
Neurotransmitters bind to receptors on the postsynaptic membrane, causing changes in the postsynaptic cell.
Neurotransmitters:
Examples:
Excitatory: Glutamate, Acetylcholine (at neuromuscular junctions).
Inhibitory: GABA, Glycine.
Modulatory: Dopamine, Serotonin, Norepinephrine.
6. Excitatory and Inhibitory Synapses
Excitatory Synapses:
Neurotransmitters (e.g., glutamate) bind to receptors that cause depolarization (e.g., by opening Na⁺ channels).
Increase likelihood of action potential generation.
Inhibitory Synapses:
Neurotransmitters (e.g., GABA) bind to receptors that cause hyperpolarization (e.g., by opening Cl⁻ channels).
Decrease likelihood of action potential generation.
Dependence on Receptors:
The same neurotransmitter can have different effects depending on the receptor type (e.g., acetylcholine excites skeletal muscle but inhibits cardiac muscle).
7. Neuronal Circuits
Types of Circuits:
Diverging Circuit: A single neuron activates multiple downstream neurons.
Converging Circuit: Multiple inputs converge onto a single neuron.
Reverberating Circuit: Neurons form a loop, allowing repetitive signals (e.g., breathing rhythm).
Parallel After-Discharge Circuit: Input travels through parallel pathways before converging.
Functions:
Control reflexes, processing, and integration of information.with different receptive fields
Adaptation & habituation1. Embryological Development of CNSThe central nervous system (CNS) develops from the neural tube formed during the third week of embryonic development.
Neurulation: The ectoderm thickens to form the neural plate, which folds to create the neural tube.
Primary brain vesicles:
Prosencephalon (forebrain)
Mesencephalon (midbrain)
Rhombencephalon (hindbrain)
These vesicles further divide to form the adult brain structures:
Forebrain → Telencephalon (cerebrum) and Diencephalon.
Midbrain → Remains as the midbrain.
Hindbrain → Metencephalon (pons, cerebellum) and Myelencephalon (medulla).
2. Protective Ventricles & Cerebrospinal Fluid (CSF)
Ventricles: Cavities in the brain where CSF is produced and circulated.
Lateral ventricles → Third ventricle → Fourth ventricle → Central canal of the spinal cord.
Cerebrospinal fluid:
Produced by the choroid plexus in the ventricles.
Functions:
Cushions and protects the brain and spinal cord.
Maintains homeostasis and removes waste.
3. Cerebral Cortex & Concept of Mapping
The cerebral cortex:
Divided into lobes: frontal, parietal, temporal, and occipital.
Responsible for higher cognitive functions, sensory processing, and voluntary motor actions.
Mapping:
Motor and sensory homunculus: Represents areas of the cortex devoted to specific body parts.
Found in the primary motor cortex (precentral gyrus) and primary sensory cortex (postcentral gyrus).
4. Diencephalon (Thalamus & Hypothalamus)
Thalamus:
Relay station for sensory and motor signals to and from the cerebral cortex.
Plays a role in consciousness and alertness.
Hypothalamus:
Regulates homeostasis (e.g., temperature, hunger, thirst).
Controls the autonomic nervous system and endocrine system via the pituitary gland.
5. Brainstem (Midbrain, Pons, Medulla Oblongata)
Midbrain:
Contains the tectum (visual and auditory reflexes) and tegmentum (motor pathways).
Pons:
Connects the cerebrum to the cerebellum and medulla.
Regulates breathing rhythm.
Medulla oblongata:
Controls vital functions such as heart rate, respiration, and blood pressure.
6. Cerebellum
Coordinates fine motor movements, balance, and posture.
Receives input from sensory systems and the spinal cord to refine motor commands.
7. Brain Protection
Cerebrospinal fluid (CSF): Cushions the CNS.
Meninges:
Dura mater: Tough outer layer.
Arachnoid mater: Middle layer with a web-like structure.
Pia mater: Inner layer adherent to the brain.
Blood-brain barrier: Prevents harmful substances from entering the brain.
8. Disorders (If Time)
Hydrocephalus: Excess CSF in the ventricles.
Stroke: Blood flow disruption to the brain.
Parkinson's disease: Degeneration of the midbrain's substantia nigra.
Alzheimer's disease: Progressive degeneration of neurons in the cortex.
Multiple sclerosis: Immune-mediated demyelination in the CNS.
Pai
Classifying receptors by stimulus type, location,
or receptor structure1. General SensesGeneral senses include:
Somatic senses: Touch, pressure, pain, temperature, proprioception.
Visceral senses: Internal organ sensations (e.g., stretch, chemical changes).
2. Receptors and Receptive Fields
Transduction: Receptors convert stimuli (e.g., mechanical, chemical, thermal energy) into electrical signals.
Receptive Fields:
Area monitored by a sensory receptor.
Smaller fields → Greater sensory acuity (e.g., fingertips).
3. Adaptation & Habituation
Adaptation: Reduced sensitivity to a constant stimulus.
Rapidly adapting receptors: Detect changes (e.g., touch, smell).
Slowly adapting receptors: Monitor ongoing stimuli (e.g., pain, pressure).
Habituation: Decreased perception due to central processing, not receptor-level changes.
4. Pain
Nociceptors: Pain receptors activated by damaging stimuli.
Fast pain: Sharp, localized (A-delta fibers).
Slow pain: Dull, diffuse (C fibers).
Modulation:
Endorphins inhibit pain transmission.
Referred pain: Perception of pain in areas distant from its source.
5. Classifying Receptors
By Stimulus Type:
Mechanoreceptors: Touch, vibration.
Thermoreceptors: Temperature.
Nociceptors: Pain.
Photoreceptors: Light.
Chemoreceptors: Chemicals.
By Location:
Exteroceptors: External stimuli (e.g., skin).
Interoceptors: Internal organs.
Proprioceptors: Joints, muscles.
By Structure:
Free nerve endings: Pain, temperature.
Encapsulated endings: Meissner’s, Pacinian corpuscles (touch, pressure).
6. Eye Structures & Functions
Outer layer:
Sclera: Protection.
Cornea: Refracts light.
Middle layer:
Choroid: Vascular supply.
Iris: Controls pupil size.
Ciliary body: Focuses lens.
Inner layer:
Retina: Contains photoreceptors.
7. Visual Receptors and Transduction of Light
Photoreceptors:
Rods: Sensitive to low light, black-and-white vision.
Cones: Detect color (red, green, blue).
Transduction:
Light converts 11-cis retinal to all-trans retinal in rhodopsin.
Leads to hyperpolarization and signal transmission to the optic nerve.
8. Visual Field & Neural Pathways
Visual field:
Left field → Right occipital cortex.
Right field → Left occipital cortex.
Pathway:
Retina → Optic nerve → Optic chiasm → Optic tracts → Thalamus (LGN) → Visual cortex.
9. Ear Structures & Functions
Outer ear:
Auricle, external auditory canal → Direct sound.
Middle ear:
Tympanic membrane, ossicles (malleus, incus, stapes) → Amplify sound.
Inner ear:
Cochlea → Hearing.
Vestibule, semicircular canals → Balance.
10. Hearing
Mechanism:
Sound waves → Tympanic membrane vibrations → Ossicles amplify → Cochlear hair cells transduce vibrations into electrical signals.
Frequency detected by specific regions of the basilar membrane.
11. Balance
Vestibular Apparatus:
Semicircular canals: Detect rotational movement.
Otolith organs (utricle and saccule): Detect linear acceleration and head position.
12. Chemical Senses (Olfaction & Taste)
Olfaction (Smell):
Olfactory receptors in the nasal epithelium detect volatile molecules.
Signals travel via the olfactory bulb to the brain.
Taste:
Taste buds on the tongue detect sweet, salty, sour, bitter, umami.
Cranial nerves (VII, IX, X) transmit signals to the brain.
13. Peripheral Nerve Repair
Regeneration:
Possible in the PNS but limited in the CNS.
Steps:
Wallerian degeneration: Axon distal to injury degenerates.
Schwann cells guide regrowth.
Challenges: Scar formation, lack of growth factors in CNS.
Eyes structures & function
visual receptors and transduction of light
visual field & neural pathways
Ears structures & function
Hearing
Balance
Chemical senses of olfaction & taste
Peripheral Nerve repair