General Organization

CNS (Brain + Spinal Cord)Peripheral NS (= PNS) Afferent Efferent Somatic Autonomic Sympathetic Parasympathetic

Protection of CNS

Mechanical Bony covering (skull, vertebrae) Meninges (dura mater, arachnoid mater, pia mater)

Chemical Blood-Brain Barrier (hypothalamus is “outside”)

Cerebral Cortex Organization

Layers I-VI

Vertical columns

Gross Anatomy of Cerebral Cortex

Four pairs of lobes (bilaterally symmetric)

Parietal Lobes

Sensory input from body surface (touch, pressure, heat, cold, pain, proprioception)

Sensory homunculus

Frontal Lobes

Voluntary movement, speech

Motor homunculus

Sensory Motor

Brain plasticity

Specific Cortical Areas

Broca’s area (formation of words)

Wernicke’s area (speech recognition)

Association areas Prefrontal association cortex Parietal-temporal-occipital association cortex Limbic association cortex (in temporal lobe)

Subcortical Structures

Basal nuclei (= basal ganglia). Lesions cause resting tremors

Thalamus

Hypothalamus

Limbic system (includes parts of cerebral cortex, basal nuclei, thalamus and hypothalamus)

MEMORY

Short term (seconds to 6 hours)

Long term (days to decades)

Consolidation

Amnesia Retrograde Anterograde

CEREBELLUM

Motor coordination: Fine movements (writing, playing musical instrument) Coarse movement (posture, walking)

Lesions cause intention tremor, poor balance, poor muscle tone, poor coordination

Brain Stem

Connects cerebrum and cerebellum to spinal cord

Includes areas that control “vital activities” (respiration, heart rate, arterial pressure, gastrointestinal activities)

Cranial nerves (12 pair; vagus)

Reticular formation and reticular activating system Controls alertness and level of attention (arousal) States of arousal: Maximal alertness Wakefulness Sleep Coma

Spinal Cord

Gray matter inside, white matter outside

Ascending and descending tracts

Spinal reflex arc

Peripheral NS: Afferent

Receptors as transducers

Sensations vs perceptions

How receptors work Stimulation usually increases Na permeability This lessens negativity of receptor cell When receptor is a neuron, this is a receptor potential When receptor isn’t a neuron, this is a generator potential Receptor and generator potentials are graded potentials at low levels of stimulus strength

Coding of Stimulus Strength

Frequency coding (afferent neuron generates action potentials at higher frequencies as stimulus strength increases)

Population coding (more afferent neurons generate action potentials as stimulus strength increases)

Adaptation Phasic receptors (respond to rate of change in stimulus strength) Tonic receptors (pain; proprioception)

Somatic vs Special Senses Special senses = taste, olfaction, vision, hearing Somatic senses are those originating on body surface (pressure, touch, heat, cold) and proprioception

Labeled lines, referred pain and phantom pain

Receptive fields and sensory acuity

Pain and Analgesia

Nociceptors (pain receptors): A-Delta fibers (fast; sensitive to heat and mechanical stimuli) C-Fibers (slow; sensitive to chemical stimuli)

Analgesia and endorphins

Central pain Chronic inflammation following injury to peripheral nerve Uninterrupted except by sleep http://www.practicalpainmanagement.com/critical-necessity-diagnose-pain-centralized

Peripheral NS – Efferent

General

Autonomics Architecture of systems (preganglionic and postganglionic cells) Sympathetic trunk (= sympathetic ganglion chain) Collateral ganglia in sympathetic system Parasympathetic ganglia

Transmitters in autonomics Preganglionic fibers are cholinergic Postganglionic fibers are cholinergic in parasympathetics, adrenergic in sympathetics

Resting outputs and autonomic tone

Autonomic dominance Sympathetic (flight or fight) Parasympathetic (vegetative)

Somatic Nervous System

Voluntary, not necessarily conscious

One neuron from CNS to effector cell (unlike autonomic)

Stimulation only, no inhibition. Motor neurons = final common pathway

Neuromuscular Junction

Neuromuscular Junction

Many terminal branches on motor neuron (one can innervate many muscle cells)

Axon terminal = “bouton” (“button”)

Motor end plate

Neuromuscular junction analogous to synapse

Usually, each action potential in motor neuron -> one action potential in muscle cell

Toxins

Black widow venom (releases ACh from cholinergic neurons)

Botulinum toxin (“botox”; blocks ACh release from boutons)

Curare (competes with ACh for cholinergic receptors)

Cholinesterase inhibitors (many insecticides, chemical warfare agents). Prevent muscles from relaxing