Nervous System | Organ Systems - MCAT

The Nervous System, Neural Cells, Neuron Membrane Potentials, Neural Synapses

Basic and Higher functions of the Nervous System

Basic: Motor, Sensory, Automatic

Higher: Cognition, Emotion, Consciousness

Somatosensory tracts

• Position, vibration and fine touch travel together in the dorsal column–medial lemniscus pathway (DCML) (aka posterior column-medial lemniscus pathway (PCML)

• Pain, temperature and gross touch travel together in the Anterolateral system aka Spinothalamic tract

Organization of the nervous system

Central Nervous System = Brain + Spinal Cord

Peripheral Nervous System = Nerves + Ganglia

• Sensory Neurons

• Motor Neurons

  • Somatic Nervous System → voluntary movement (ft. skeletal muscle)

  • Autonomic Nervous System → involuntary movement

    • Sympathetic Nervous System

    • Parasympathetic Nervous System

Sympathetic vs. Parasympathetic

• Functions

• Neurotransmitters used

• Position of ganglia and length of nerves

Sympathetic → Fight or Flight

• Increase heart rate and blood pressure, Direct blood flow to muscles

• Preganglionic neurons (primarily) use Acetylcholine, Postganglionic neurons use Norepinephrine

• Ganglia in middle of spinal cord

• 1st neuron sends short axon to 2nd neuron, 2nd neuron sends long axon to target cells

Parasympathetic → Rest and Digest

• Decrease heart rate and blood pressure, Direct blood flow to intestines

• Neurons use Acetylcholine

• Ganglia at bottom and top of spinal cord

• 1st neuron sends long axon to 2nd neuron, 2nd neuron sends short axon to target cells

Afferent vs. Efferent

From PNS to CNS vs. From CNS to PNS

Arrive vs. Efflux

Lower motor neuron vs. Upper motor neuron

UMNs control LMNs, which control skeletal muscle

• UMNs originate in cerebral cortex and brainstem, LMNs originate in brainstem and spinal cord

Motor unit

Lower motor neuron + all the cells it controls

SAME DAVE

Sensory is Afferent, Motor is Efferent

Dorsal is Afferent, Ventral is Efferent (regarding spinal nerves)

Lower Motor Neuron Signs

Atrophy = shrinkage

Fasciculation = involuntary twitching

Hypotonia = floppage

Hyporeflexia = weaker or absent reflex response

Upper Motor Neuron Signs

Hypertonia

Hyperreflexia

Clonus = rhythmic contraction of antagonist muscles (ft. muscle stretch reflex?)

Extensor Plantar Response = + Babinski sign

Draw a diagram of the developing brain

Corticospinal vs. Corticobulbar tracts

2 paths thru which Upper Motor Neurons get to Lower Motor Neurons

• To reach LMNs in the spinal cord, UMN axons cross over to other side where medulla meets spinal cord

• To reach LMNs in brainstem, UMN axons may either cross or not cross

Muscle stretch reflex

Muscle contraction in response to stretch

Protects muscle from tearing, helps with posture

• eg. knee-jerk reaction: hitting patellar tendon stretches quadriceps femoris muscle, muscle spindles detect stretch and send signal to lower motor neurons in spinal cord to contract quadriceps and to inhibitory neurons to tell LMNs to relax hamstrings

Neural stem cells vs. Neural crest cells

neural cells in CNS are derived from these

vs.

neural cells in PNS are derived from these

Glial cell types

Astrocytes = structural support, scar formation, provide lactate, end-feet are part of blood brain barrier, help clear neurotransmitters from synapse

Ependymal cells = produce cerebrospinal fluid, create leaky barrier b/t cerebrospinal and interstitial fluid

Microglia = macrophages (inflammation converts from resting to active state)

Oligodendrocytes = myelination in CNS (can myelinate several per cell)

Schwann cells = myelination in PNS (can only myelinate once per cell)

Development of neuron

• Neural stem/crest cell differentiates into Neuroblast (which can only differentiate into neurons)

• neuroblast migrates to final location of soma

• there, it extends axon with growth cone that helps find target = unipolar neuron

• unipolar neuron differentiates into bipolar, multipolar, or pseudounipolar mature neuron

Notable neurotransmitters

• Functions and locations

• Structural classes they belong to

Amino acids: Glutamate, GABA, Glycine

Monoanimes: Serotonin, Histamine, Dopamine, Epinephrine, Norepinephrine

Peptides: Endorphins

Others: Acetylcholine

Glutamate is main excitatory NT in the nervous system; important for learning, memory and cognitive function

GABA is main inhibitory NT in the brain: regulates anxiety, sleep, stress and muscle tone

Glycine is main inhibitory NT in the spinal cord and brainstem: regulates motor control, pain processing and auditory signals

Serotonin regulates mood, sleep, digestion, nausea, wound healing, bone health, sex drive. Primary building block for melatonin low levels linked to depression

Histamine is produced by neurons in the hypothalamus and regulates sleep-wake cycle, appetite, cognitive function

Dopamine is important for reward and motivation, motor control, cognition and attention

Epinephrine regulates metabolism, attention, sleep-wake cycle, panic and excitement (small role as neurotransmitter)

Norepinephrine is main NT in sympathetic nervous system; increases attentional/arousal, regulates sleep-wake cycle, mood and memory, constricts blood vessels (significantly larger role than epinephrine)

Endorphins: natural painkillers, inhibitory NTs released during stress, physical exertion & pleasurable activities 😛

Acetylcholine: enables communication between neurons and muscle (both voluntary and involuntary), regulates memory, learning and attention

Good if u can name 2 things about each NT

(If not specified as excitatory or inhibitory, they probably do a good amount of both)

Frontal Lobe

High-level thinking

• Decision-making

• Planning and organizing

• Impulse control

• working memory

Voluntary movement

Speech (incl. broca’s area)

Occipital Lobe

Visual processing

Parietal Lobe

Sensory processing (somatosensation)  

• touch, pain, temperature, position / movement

Spatial awareness

• Data moves from occipital → parietal via dorsal stream 

• Motion, depth, spatial location 

Sensory integration

Math and symbols

Temporal Lobe

Auditory processing 

Language (incl. wernicke’s area)

Memory (incl. hippocampus)

Emotions

Visual recognition 

• Data moves from occipital → temporal via ventral stream 

• Form, color, detailed object recognition

Cerebellum

Coordination of voluntary movement 

Balance and posture 

Muscle tone (normal state of continuous light tension) 

Cognition 

• Attention, language processing, working memory 

Emotion

Limbic system

• what it is

• component parts

group of connected structures deep in the brain that control emotions, memory, hunger and basic survival drives

includes

• thalamus

• hypothalamus

• cingulate gyrus

• hippocampus

• amygdala

Thalamus

relay and processing center

receives and filters sensory*, motor and limbic signals, then sends them to cerebral cortex

*all senses except smell

Hypothalamus

Maintains homeostasis and links nervous to endocrine system

Regulates temperature, hunger, thirst, sleep-wake cycle, blood pressure, heart rate and digestion

Directs pituitary gland

Hippocampus

memory

forms new declarative memories

transfers short term data to long term storage

constructs mental maps for navigation

helps link emotion to memory

Amygdala

edgy

processes fear and anger, initiates “fight or flight”

helps read facial expressions and social cues

helps link emotion to memory

Midbrain

Visual and auditory processing, eye movement and body movement

Bridge that connects forebrain and lower brain

Pons

Bridge between cerebrum, cerebellum and spinal cord

regulates breathing rhythm, sleep states, facial movements and sensations

coordinates voluntary movement, fine motor control and posture

Medulla oblongata

Vitals and reflexes

Basic functions: breathing, heartbeat, blood pressure

Basic Reflexes: coughing, sneezing, swallowing, gagging, vomiting

also is point of crossover for motor nerves