Overview
This lecture covers the structure, divisions, and key functions of the nervous system, including the anatomy of the central and peripheral systems, types of neurons and support cells, nerve signal transmission, major brain regions, and reflex actions.
Divisions and Functions of the Nervous System
- The nervous system divides into the central nervous system (CNS: brain and spinal cord) and peripheral nervous system (PNS: nerves outside the CNS).
- Functions include sensory input, integration of information, muscle and gland control, maintaining homeostasis, and establishing mental activity such as emotions.
- The sensory division receives input; the motor division sends signals to muscles and glands.
- The somatic nervous system controls skeletal muscles; the autonomic nervous system controls cardiac and smooth muscle.
- The enteric nervous system manages digestive tract functions.
Structure and Types of Neurons and Glial Cells
- Neurons receive, process, and transmit signals; their main parts are the cell body, dendrites, and axon.
- Multipolar neurons have multiple dendrites; bipolar have one dendrite and one axon; pseudo-unipolar have one process that branches.
- Glial cells support neurons: astrocytes (CNS) form the blood-brain barrier, ependymal cells line brain cavities, microglia perform immune functions, oligodendrocytes (CNS) and Schwann cells (PNS) create myelin sheaths.
- Myelinated axons conduct signals faster; nodes of Ranvier are gaps in myelin where ions move in/out.
- Gray matter contains mostly unmyelinated neurons, white matter contains myelinated axons.
Signal Transmission and Synapses
- Action potentials travel faster in larger-diameter, myelinated axons.
- Synapses are gaps where neurotransmitters (e.g., acetylcholine, norepinephrine) transfer signals between neurons.
- Acetylcholinesterase breaks down acetylcholine.
- Pathways: converging (many to one neuron) and diverging (one to many neurons).
Gross Anatomy of CNS and Reflexes
- The spinal cord is protected by the vertebral column, with gray matter (center, butterfly-shaped) and white matter (outer).
- Posterior horns have interneurons, anterior horns have somatic neurons, lateral horns have autonomic neurons; central canal contains fluid.
- Reflexes are involuntary responses; reflex arc steps: receptor → sensory neuron → interneuron → motor neuron → effector organ.
- Examples: stretch reflex (knee jerk), withdrawal reflex (pulling away from pain).
Brain Regions and Functions
- Brainstem (medulla oblongata, pons, midbrain): controls vital involuntary functions (heart rate, breathing, reflexes).
- Cerebellum: responsible for balance, coordination, and fine motor control.
- Diencephalon (thalamus: sensory relay/moods; hypothalamus: hormone/pituitary control; epithalamus: smell response, houses pineal gland).
- Cerebrum: largest part, divided into left/right hemispheres (analytical vs. creative), consists of lobes for specific functions.
- Lobes: frontal (voluntary movement, mood), parietal (sensory input), occipital (vision), temporal (hearing, memory).
- Speech areas: Wernicke's (sensory comprehension), Broca's (motor speech formation).
Memory and Brain Waves
- Working memory is short and task-related; short-term lasts days; long-term forms by consolidation.
- Declarative memory stores facts; procedural memory stores skills.
- Limbic system processes emotions, motivation, and memory.
- Brain waves: alpha (awake/relaxed), beta (intense activity), delta (deep sleep), theta (children).
Brain and Spinal Cord Protection
- Meninges: dura mater (outer), arachnoid mater (middle), pia mater (inner).
- Cerebrospinal fluid (produced by ependymal cells) cushions the brain and spinal cord.
Autonomic and Enteric Nervous Systems
- Autonomic NS: sympathetic (activates physical activity), parasympathetic (controls rest/digestion).
- Enteric NS: controls digestive tract, communicates with CNS via sensory/motor neurons.
Key Terms & Definitions
- Neuron — cell that transmits nerve signals.
- Glial cell — supportive cell in the nervous system.
- Myelin sheath — insulating layer around axons that increases signal speed.
- Synapse — junction between neurons.
- Reflex — involuntary, fast response to stimuli.
- Cerebrospinal fluid (CSF) — fluid cushioning the CNS.
- Meninges — protective layers around brain and spinal cord.
- Limbic system — brain region for emotion and memory.
Action Items / Next Steps
- Review the posted quiz schedule on Teams.
- Send lecture-related questions via Teams chat.
- Study diagrams of brain regions, neuron types, and spinal cord cross-sections.