Neural Control and Coordination Exercise Solutions | KalviGavani

| Feature | Sensory (Afferent) Neuron | Motor (Efferent) Neuron | |---|---|---| | Direction | From receptor to CNS | From CNS to effector | | Dendrite | Long (from receptor) | Short | | Axon | Short | Long | | Cell body | In the dorsal root ganglion | In the CNS or ventral horn | | Function | Carry sensory information | Carry motor commands | | Example | Neuron from skin to spinal cord | Neuron from spinal cord to muscle |

A reflex arc is the pathway followed by a reflex action. Its components are: 1. Receptor: Detects the stimulus (e.g., heat receptor in skin) 2. Sensory neuron: Carries impulse from receptor to spinal cord 3. Interneuron (relay neuron): Connects sensory and motor neurons in the spinal cord 4. Motor neuron: Carries impulse from spinal cord to effector 5. Effector: Responds (e.g., muscle contracts, gland secretes)

The hypothalamus is a small but vital part of the brain (in the forebrain) that: 1. Regulates body temperature (shivering, sweating) 2. Controls hunger and thirst 3. Regulates sleep-wake cycle 4. Controls the pituitary gland (master gland of endocrine system) 5. Maintains homeostasis (internal balance) 6. Regulates emotional responses (anger, pleasure, fear)

| Feature | Sympathetic | Parasympathetic | |---|---|---| | Effect | Fight or flight | Rest and digest | | Heart rate | Increases | Decreases | | Pupil | Dilates | Constricts | | Digestion | Decreases | Increases | | Breathing | Bronchodilation | Bronchoconstriction | | Neurotransmitter | Noradrenaline | Acetylcholine |

Structure of a Neuron: A neuron has three main parts: 1. Cell body (cyton/soma): Contains the nucleus and Nissl's granules (clusters of rough ER). It processes incoming signals from dendrites. 2. Dendrites: Short, branched processes that receive impulses from other neurons and transmit them toward the cell body. 3. Axon: A single, long process that transmits impulses away from the cell body. It may be covered by a myelin sheath (produced by Schwann cells) with gaps called Nodes of Ranvier. The axon ends in branched terminals containing synaptic vesicles with neurotransmitters. Conduction of Nerve Impulse: 1. Resting Potential: - At rest, the neuron membrane has a potential difference of -70 mV (inside negative) - Maintained by the Na⁺/K⁺ pump (3 Na⁺ out, 2 K⁺ in) - More Na⁺ outside, more K⁺ inside - The membrane is said to be polarised 2. Depolarisation (Action Potential): - When a stimulus reaches threshold, Na⁺ channels open - Na⁺ rushes INTO the cell (down concentration gradient) - Membrane potential reverses: -70 mV → +30 mV - The membrane is depolarised 3. Repolarisation: - Na⁺ channels close, K⁺ channels open - K⁺ rushes OUT of the cell - Membrane potential returns: +30 mV → -70 mV - The membrane is repolarised 4. Refractory Period: - Brief period when the neuron cannot generate another impulse - Na⁺/K⁺ pump restores original ion distribution - Ensures impulse travels in one direction 5. Saltatory Conduction: - In myelinated neurons, the impulse jumps from one Node of Ranvier to the next - This is much faster than continuous conduction - Myelinated neurons conduct impulses up to 50 times faster than unmyelinated neurons

The human brain is the command centre of the nervous system. It weighs about 1.4 kg and is protected by the cranium and meninges (dura mater, arachnoid, pia mater). 1. Forebrain: Cerebrum: - Largest part of the brain; divided into left and right hemispheres connected by the corpus callosum - Outer layer: Cerebral cortex (grey matter) — contains cell bodies - Inner layer: White matter — contains axons - Functions: Thinking, reasoning, memory, learning, voluntary actions, speech, emotions - Each hemisphere controls the opposite side of the body (left hemisphere → right side, right hemisphere → left side) Thalamus: - Located below the cerebrum - Acts as a relay station for sensory and motor signals to the cerebrum - Filters and processes sensory information (except smell) Hypothalamus: - Located below the thalamus - Controls body temperature, hunger, thirst, sleep-wake cycle - Controls the pituitary gland (master endocrine gland) - Maintains homeostasis - Controls emotional responses 2. Midbrain: - Located between the forebrain and hindbrain - Contains the cerebral aqueduct connecting the third and fourth ventricles - Controls visual and auditory reflexes - Connects the forebrain to the hindbrain 3. Hindbrain: Cerebellum: - Located below the cerebrum and behind the brainstem - Functions: Balance, posture, coordination of voluntary movements - Damage causes uncoordinated movements and loss of balance Pons: - Connects the cerebellum to the medulla - Regulates breathing (works with the medulla) - Contains relay centres for facial expressions Medulla Oblongata: - Connects the brain to the spinal cord - Controls vital involuntary functions: breathing, heart rate, blood pressure - Contains reflex centres: coughing, sneezing, vomiting, swallowing - Damage can be fatal (controls breathing and heart rate)

A synapse is the junction between two neurons (or a neuron and an effector). Most synapses are chemical — they use neurotransmitters to transmit impulses. Structure of a Chemical Synapse: 1. Presynaptic membrane: Membrane of the axon terminal (sending neuron) 2. Synaptic cleft: The gap between the two neurons (~20-30 nm) 3. Postsynaptic membrane: Membrane of the receiving neuron (dendrite or cell body) Mechanism of Synaptic Transmission: Step 1: Arrival of Action Potential: The action potential (nerve impulse) reaches the axon terminal of the presynaptic neuron. Step 2: Calcium Influx: The depolarisation opens voltage-gated calcium channels in the presynaptic membrane. Ca²⁺ ions flow INTO the axon terminal from the synaptic cleft. Step 3: Vesicle Fusion: Ca²⁺ triggers synaptic vesicles (containing neurotransmitters) to fuse with the presynaptic membrane. Step 4: Neurotransmitter Release: The synaptic vesicles release neurotransmitters (e.g., acetylcholine) into the synaptic cleft through exocytosis. Step 5: Receptor Binding: The neurotransmitters diffuse across the synaptic cleft and bind to specific receptors on the postsynaptic membrane. Step 6: Postsynaptic Response: Binding of neurotransmitters opens ion channels on the postsynaptic membrane: - Excitatory synapse: Na⁺ channels open → depolarisation (EPSP — excitatory postsynaptic potential) - Inhibitory synapse: Cl⁻ or K⁺ channels open → hyperpolarisation (IPSP — inhibitory postsynaptic potential) Step 7: Termination: The neurotransmitter is quickly removed from the synaptic cleft by: - Enzymatic degradation: Acetylcholinesterase breaks down acetylcholine - Reuptake: Neurotransmitters are taken back into the presynaptic neuron - Diffusion: Neurotransmitters diffuse away from the synapse This ensures the signal is brief and precise. Without removal, the postsynaptic neuron would be continuously stimulated.