neuro exam2

Chapter 4: Neural Communication

🧩 Basic Neuron Structure

  • Neuron: the main communication cell of the nervous system.

  • Parts:

    • Dendrites: receive signals (input).

    • Cell body (soma): processes info.

    • Axon: sends electrical signals away from the soma.

    • Axon terminals (boutons): release neurotransmitters to communicate with the next cell.

  • Where action potential starts: at the axon hillock (trigger zone).

🧠 How a Neuron Works

  • Signals travel dendrite → soma → axon → terminal.

  • Depolarization: sodium (Na⁺) channels open → inside becomes more positive.

  • Repolarization: potassium (K⁺) leaves → returns cell to negative.

  • Sodium-potassium pump: restores resting potential by moving 3 Na⁺ out, 2 K⁺ in.

⚡ Action vs. Graded Potentials

  • Graded potential: small change, can build up (like tapping a key).

  • Action potential: all-or-none spike once threshold is reached (like hitting “send”).

  • Propagation: AP moves down axon by opening Na⁺ channels one after another.

🔗 Synapse & Neurotransmission

  • Synapse: junction between neurons.

  • Neurotransmitters cross the gap and bind to receptors on the next neuron.

  • Excitatory → increases likelihood of firing (e.g., glutamate).

  • Inhibitory → decreases likelihood (e.g., GABA).

  • A neuron is either excitatory or inhibitory — not both.

💊 Key Neurotransmitters

  • Acetylcholine (ACh): motor control, muscle contraction.

  • Dopamine: reward, movement, motivation.

  • Serotonin: mood, sleep.

  • Norepinephrine: alertness, stress.

🧠 Types of Neurons

  • Multipolar: many dendrites, one axon — motor neurons, most common.

  • Bipolar: one dendrite + one axon — found in retina, olfactory system.

  • Unipolar: single projection — sensory neurons.

⚙ Other Terms

  • Projection neurons: send signals long distances.

  • Local neurons: communicate within a region.

  • Afferent = sensory, Efferent = motor.

  • Motor neurons in cortex = multipolar.

Chapter 5: Sensory Pathways

🧭 Overview

  • Transducer: converts one form of energy (like sound or light) into neural signals.

  • Somatosensory pathways: bring touch, temperature, and pain info to the brain.

🧩 Orders of Neurons

  1. First-order neuron: detects stimulus (in skin/sense organ).

  2. Second-order neuron: in spinal cord or brainstem; sends info to thalamus.

  3. Third-order neuron: in thalamus; sends info to cortex.

🌡 Sensory Tracts

  • Dorsal column–medial lemniscus: fine touch, vibration, proprioception.

  • Spinothalamic tract: pain and temperature.

  • Trigeminothalamic tract: sensory info from the face (cranial nerves).

👁 Optic System

  • Photoreceptors (rods/cones): transducers that convert light to neural signals.

  • Optic chiasm: where nasal retinal fibers cross — this crossing allows both eyes to share visual info.

    • If severed, results in bitemporal hemianopsia (loss of peripheral vision in both eyes).

🧠 Tonotopic Organization

  • In the auditory system: different sound frequencies are mapped to specific spots in the cochlea and auditory cortex.

🌀 Cochlear Fluids

  • Perilymph: in scala vestibuli & scala tympani.

  • Endolymph: in scala media.

  • These help transmit sound vibrations through the cochlea.

Chapter 6: Motor Pathways

🦵 Motor Unit

  • Motor unit = 1 motor neuron + all the muscle fibers it controls.

  • Controls the force and precision of movement.

⚡ Neuromuscular Junction

  • Where a motor neuron communicates with a muscle fiber.

  • Uses acetylcholine (ACh) to trigger muscle contraction.

⬆ Upper vs. ⬇ Lower Motor Neurons

  • Upper Motor Neuron (UMN): from cortex → brainstem/spinal cord.

  • Lower Motor Neuron (LMN): from brainstem/spinal cord → muscle.

    • LMN = “final common pathway.”

  • Damage:

    • UMN lesion: spasticity, hyperreflexia.

    • LMN lesion: weakness, atrophy, fasciculations.

🧩 Pyramidal System (Voluntary Movement)

  • Direct control from cortex to muscle.

  • Tracts:

    • Corticospinal tract: cortex → spinal cord (controls limbs/body).

    • Corticobulbar (corticonuclear) tract: cortex → cranial nerves (controls face/speech muscles).

  • Type of neurons here: multipolar motor neurons.

⚙ Extrapyramidal System (Automatic/Postural Control)

  • Indirect control — modulates movement, posture, and reflexes.

  • Tracts include:

    • Tectospinal tract: reflexive head/neck movement toward visual or auditory stimuli (e.g., turning to a loud noise).

    • Vestibulospinal tract: maintains balance and posture using input from the inner ear.

    • Reticulospinal tract: helps with muscle tone and automatic movements (walking posture).

    • Rubrospinal tract: assists fine motor control of limbs.

🎯 Cerebellum

  • Coordinates timing, precision, and balance of movement.

  • Does not initiate movement — it fine-tunes it.

  • Each cerebellar hemisphere controls the same (ipsilateral) side of the body.

    • Lesion → loss of coordination on that same side.