Neural Control and Coordination — Revision Notes

⚡ 30-Second Revision

Neuron: — Cell body, dendrites (receive), axon (transmit). \n- Myelin Sheath: Insulates axon, speeds conduction (saltatory). \n- Resting Potential: $-70,\text{mV}$, maintained by Na+/K+ pump (3Na+ out, 2K+ in) and differential permeability (more K+ efflux). \n- Action Potential: \n - Depolarization: Na+ influx (voltage-gated Na+ channels open). \n - Repolarization: K+ efflux (voltage-gated K+ channels open). \n - All-or-None: Fires fully if threshold reached. \n- Synapse: Presynaptic neuron \rightarrow Synaptic cleft \rightarrow Postsynaptic neuron. \n- Neurotransmitter Release: Triggered by Ca2+ influx into presynaptic terminal. \n- CNS: Brain (forebrain, midbrain, hindbrain) + Spinal cord. \n- Forebrain: Cerebrum (thought, voluntary), Thalamus (relay), Hypothalamus (homeostasis, temp, thirst, hunger). \n- Hindbrain: Pons (respiration), Cerebellum (balance, coordination), Medulla (vital reflexes: HR, BP, breathing). \n- PNS: Somatic (voluntary) + Autonomic (involuntary). \n- ANS: Sympathetic ('fight/flight') vs. Parasympathetic ('rest/digest'). \n- Reflex Arc: Receptor \rightarrow Afferent \rightarrow (Interneuron) \rightarrow Efferent \rightarrow Effector.

2-Minute Revision

Neural control and coordination are orchestrated by the nervous system, which uses neurons for rapid communication. Neurons transmit electrochemical signals called action potentials. At rest, the neuron maintains a negative internal charge (resting potential) due to the Na+/K+ pump and differential ion permeability.

When stimulated past a threshold, voltage-gated Na+ channels open, causing depolarization (Na+ influx). This is followed by repolarization as K+ channels open and K+ effluxes. These impulses propagate along the axon, faster in myelinated axons via saltatory conduction.

Communication between neurons occurs at synapses, where neurotransmitters, released due to Ca2+ influx, bind to postsynaptic receptors, causing excitation or inhibition. \n\nThe nervous system is divided into the Central Nervous System (CNS) – brain and spinal cord – and the Peripheral Nervous System (PNS) – all other nerves.

The brain is the control center, with the cerebrum for higher functions, cerebellum for coordination, hypothalamus for homeostasis, and medulla for vital reflexes. The PNS includes the somatic system for voluntary control and the autonomic system for involuntary functions, further split into sympathetic ('fight or flight') and parasympathetic ('rest and digest') divisions.

Reflex actions are rapid, involuntary responses mediated by a reflex arc, bypassing conscious brain processing for speed.

5-Minute Revision

The nervous system, the body's rapid communication network, is built upon neurons. Each neuron has dendrites to receive signals, a cell body for processing, and an axon to transmit signals. The axon can be myelinated, allowing for faster, saltatory conduction of nerve impulses.

A nerve impulse, or action potential, is an 'all-or-none' electrical event. It begins with a resting membrane potential (around $-70,\text{mV}$), maintained by the Na+/K+ pump and selective ion permeability.

Upon reaching a threshold stimulus, voltage-gated Na+ channels open, causing rapid depolarization (Na+ influx). This is quickly followed by repolarization as voltage-gated K+ channels open, allowing K+ efflux.

\n\nNeurons communicate at synapses. In chemical synapses, an arriving action potential at the presynaptic terminal triggers Ca2+ influx, which in turn causes synaptic vesicles to release neurotransmitters into the synaptic cleft.

These neurotransmitters bind to specific receptors on the postsynaptic membrane, leading to either excitation (EPSP) or inhibition (IPSP) of the postsynaptic neuron. \n\nThe nervous system is structurally organized into the Central Nervous System (CNS), comprising the brain and spinal cord, and the Peripheral Nervous System (PNS), which includes all nerves extending from the CNS.

The brain is functionally divided: the forebrain (cerebrum for higher thought, thalamus for relay, hypothalamus for homeostasis like temperature, thirst, hunger), midbrain (visual/auditory reflexes), and hindbrain (pons for respiration, cerebellum for balance and coordination, medulla for vital involuntary functions like heart rate and breathing).

The spinal cord serves as a reflex center and a pathway for signals. The PNS has a somatic division (voluntary control of skeletal muscles) and an autonomic division (involuntary control of internal organs).

The autonomic nervous system is further split into the sympathetic ('fight or flight' responses like increased heart rate, dilated pupils) and parasympathetic ('rest and digest' responses like decreased heart rate, stimulated digestion) systems, which generally have antagonistic effects.

Reflex actions, such as withdrawing a hand from a hot object, are rapid, involuntary responses mediated by a reflex arc, a pathway involving a receptor, sensory neuron, (interneuron), motor neuron, and effector, often bypassing conscious brain processing for speed and protection.

Prelims Revision Notes

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Neuron Structure: — \n * Cell Body (Soma): Nucleus, Nissl's granules (RER + ribosomes). \n * Dendrites: Receive signals, transmit towards cell body. \n * Axon: Transmit signals away from cell body. \n * Myelin Sheath: Formed by Schwann cells (PNS) or oligodendrocytes (CNS). Insulates, speeds conduction. \n * Nodes of Ranvier: Gaps in myelin, site of action potential generation in myelinated axons (saltatory conduction). \n2. Nerve Impulse (Action Potential): \n * Resting Membrane Potential (RMP): $-70,\text{mV}$. Maintained by Na+/K+ pump (3Na+ out, 2K+ in) and higher K+ permeability. \n * Depolarization: Stimulus \rightarrow Threshold \rightarrow Voltage-gated Na+ channels open \rightarrow Na+ influx \rightarrow Inside becomes positive. \n * Repolarization: Na+ channels inactivate \rightarrow Voltage-gated K+ channels open \rightarrow K+ efflux \rightarrow Inside becomes negative again. \n * Hyperpolarization: Brief overshoot below RMP due to slow K+ channel closure. \n * Refractory Period: Period of unresponsiveness, ensures unidirectional propagation. \n3. Synaptic Transmission: \n * Chemical Synapse: Action potential \rightarrow Presynaptic terminal depolarization \rightarrow Voltage-gated Ca2+ channels open \rightarrow Ca2+ influx \rightarrow Synaptic vesicles fuse \rightarrow Neurotransmitter release into synaptic cleft. \n * Neurotransmitters: Bind to postsynaptic receptors \rightarrow Ion channels open \rightarrow EPSP (depolarization, excitatory) or IPSP (hyperpolarization, inhibitory). \n * Examples: Acetylcholine (excitatory/inhibitory), GABA (inhibitory), Glutamate (excitatory). \n4. Central Nervous System (CNS): \n * Brain: \n * Forebrain: Cerebrum (largest, voluntary, thought, memory), Thalamus (sensory/motor relay), Hypothalamus (homeostasis: temp, thirst, hunger, endocrine link). \n * Midbrain: Connects forebrain to hindbrain, visual/auditory reflexes (corpora quadrigemina). \n * Hindbrain: Pons (respiration, sleep), Cerebellum (balance, coordination, posture), Medulla Oblongata (vital centers: heart rate, respiration, BP, swallowing, vomiting). \n * Spinal Cord: Reflex center, conduction pathway. \n5. Peripheral Nervous System (PNS): \n * Somatic Nervous System: Voluntary control, skeletal muscles. \n * Autonomic Nervous System (ANS): Involuntary control (smooth muscle, cardiac muscle, glands). \n * Sympathetic: 'Fight or flight' (increases HR, dilates pupils, inhibits digestion). \n * Parasympathetic: 'Rest and digest' (decreases HR, constricts pupils, stimulates digestion). \n6. Reflex Action & Arc: \n * Reflex Action: Rapid, involuntary response. \n * Reflex Arc: Pathway: Receptor \rightarrow Afferent neuron \rightarrow (Interneuron in CNS) \rightarrow Efferent neuron \rightarrow Effector.

Vyyuha Quick Recall

To remember the main functions of the Hypothalamus: Thirst, Hunger, Emotions, Temperature, Sleep-wake cycle. (THE TS)