Neural Control and Coordination

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Neural Control and Coordination The nervous system provides an organised network of point-to-point connections for a quick coordination. The endocrine system provides chemical integration through hormones. Neurons as Structural and Functional Units Neurons are excitable cells due to polarised membranes. They conduct electrical impulses. Each neuron has a cell body (cyton), dendrites, and axon. Cell body: Contains cytoplasm with cell organelles and Nissl's granules. Dendrites: Short fibres, project out of the cell body, transmit impulses towards the cell body. Axon: Long fibre, distal end branched, each branch ends in a synaptic knob containing neurotransmitters. Transmits impulses away from the cell body to another neuron or effector organ. Types of Neurons Multipolar: One axon, two or more dendrites (e.g., cerebral cortex). Bipolar: One axon, one dendrite (e.g., retina of eye). Unipolar: Cell body with one axon only (e.g., embryonic stage). Types of Axons Myelinated: Axons covered with Schwann cells, forming a myelin sheath. Gaps are called Nodes of Ranvier. Found in spinal and cranial nerves. Non-myelinated: Schwann cells do not form a myelin sheath. Found in autonomous and somatic neural systems. Generation and Conduction of Nerve Impulse Neurons are excitable cells due to their polarised membrane. Resting potential: Membrane is more permeable to $K^+$ ions and impermeable to $Na^+$ ions. $Na^+/K^+$ pump actively transports $3 Na^+$ out for $2 K^+$ in. Results in a negative charge inside and positive charge outside the membrane. Resting potential is $-70mV$. Depolarisation (Action Potential): Stimulus causes $Na^+$ channels to open, $Na^+$ rushes in. Inside becomes positive, outside negative. Potential becomes $+30mV$ to $+40mV$. Repolarisation: $K^+$ channels open, $K^+$ rushes out. $Na^+$ channels close. Restores negative charge inside and positive outside. $Na^+/K^+$ pump re-establishes ion gradients. Conduction: Impulse propagates along the axon as a wave of depolarisation and repolarisation. Transmission of Impulses Occurs at synapses between two neurons. Synapse: Formed by pre-synaptic neuron, synaptic cleft, and post-synaptic neuron. Electrical synapse: Pre- and post-synaptic membranes are in close proximity. Impulse transmission is similar to single neuron conduction. Faster, less common. Chemical synapse: Synaptic cleft present. Neurotransmitters (e.g., acetylcholine) released from pre-synaptic terminal. Neurotransmitters bind to receptors on post-synaptic membrane, generating a new potential. Can be excitatory or inhibitory. Central Neural System (CNS) Includes the brain and spinal cord. Site of information processing and control. Brain Protected by skull and meninges (dura mater, arachnoid, pia mater). Divided into forebrain, midbrain, and hindbrain. Forebrain Cerebrum: Largest part. Two cerebral hemispheres connected by corpus callosum. Outer layer (cerebral cortex) is grey matter, inner part is white matter. Cortex has motor areas, sensory areas, and large association areas (memory, communication). Thalamus: Major coordinating centre for sensory and motor signalling. Hypothalamus: Controls body temperature, urge for eating and drinking. Contains neurosecretory cells that secrete hormones. Midbrain Located between thalamus/hypothalamus and pons. Dorsal portion has four round swellings (corpora quadrigemina) involved in visual and auditory reflexes. Hindbrain Pons: Fibre tracts that interconnect different regions of the brain. Cerebellum: Highly convoluted surface for more neurons. Maintains body posture and balance. Medulla Oblongata: Connected to spinal cord. Controls respiration, cardiovascular reflexes, gastric secretions. Brainstem = Midbrain + Pons + Medulla. Peripheral Neural System (PNS) Comprises all nerves originating from CNS. Divided into Somatic Neural System (SNS) and Autonomic Neural System (ANS). SNS: Transmits impulses from CNS to skeletal muscles. ANS: Transmits impulses from CNS to involuntary organs and smooth muscles. Sympathetic: "Fight or flight" response. Parasympathetic: "Rest and digest" response.