Chapter 35 Slides

NERVOUS SYSTEM Lecture Overview

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Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Adaptation from Biology 2e and Xavier University of Louisiana Biology 1240.

Nerves and Nervous Systems

Organisms respond to environmental stimuli via the Sensory System, which allows for the detection of changes in the environment (stimulus). There are two primary response systems in the body:

• Endocrine System: Utilizes hormones to relay information throughout the body over a long span of time.

• Nervous System: Utilizes neurons to transmit electrical signals rapidly.

Human Nervous System

• Central Nervous System (CNS): Comprises the brain and spinal cord; it processes sensory information and initiates responses.

• Peripheral Nervous System (PNS): Consists of cranial and spinal nerves that gather sensory information and transmit it to the CNS for processing.

Functions of the Nervous System

1. Sensory input (PNS): Collects information from the environment.

2. Integration and decision-making (CNS): Processes information and formulates responses.

3. Motor output (PNS): Delivers commands from the CNS to execute responses in the body.

Neurons

• Components:

  • Dendrites: Receive stimuli from the environment.

  • Cell Body: Contains the nucleus and organelles necessary for cell function.

  • Axon: Conducts electrical signals away from the cell body towards other neurons or muscles.

• Types of Neurons:

  • Motor Neurons: Transmit signals from the CNS to muscles and glands, facilitating movement and secretion.

  • Sensory Neurons: Carry signals from sensory receptors to the CNS, allowing perception of stimuli.

  • Interneurons: Connect neurons within the CNS and are involved in reflexes and higher-level processing.

Glial Cells

• These cells support and protect neurons, existing in a 10:1 ratio to neurons. Many brain tumors originate from glial cells.

• Types of Glial Cells:

  • Schwann Cells: Form myelin sheath in the peripheral nervous system.

  • Oligodendrocytes: Create myelin sheath in the central nervous system.

  • Astrocytes: Provide structural support and regulate nutrient flow.

  • Microglia: Act as the immune defense in the CNS.

Neuronal Communication

• Neurons communicate via electrical signals, with a resting membrane potential of -70mV.

• Action Potential: A rapid change in membrane potential that occurs when depolarization reaches the threshold of -55 mV, leading to the firing of a signal.

Signal Transmission

• The nerve impulse travels along the axon via action potentials, which are accelerated by the presence of myelin sheath through a process known as saltatory conduction.

Synaptic Transmission

• The action potential prompts the release of neurotransmitters into the synaptic cleft, where they can excite or inhibit the postsynaptic cells, thereby influencing their activity.

Brain and Spinal Cord

• Both the brain and spinal cord are protected by bone and meninges, and they are cushioned by cerebrospinal fluid to absorb shock.

• Cerebrum: Largest part of the brain, primarily responsible for cognitive functions and processing sensory information.

• Cerebellum: Coordinates voluntary movements and maintains posture.

• Brain Stem: Regulates vital functions such as heart rate and breathing, and controls reflexes.

Peripheral Nervous System

• Somatic System: Controls skeletal muscles, allowing for conscious movement and voluntary actions.

• Autonomic System: Regulates involuntary functions; further divided into:

  • Sympathetic: Activates the fight-or-flight response.

  • Parasympathetic: Controls 'rest and digest' processes, promoting maintenance and conservation of energy.

Neurodegenerative Disorders

• These disorders involve progressive neuronal death and include conditions such as Alzheimer’s and Parkinson’s diseases, which significantly impair cognitive and motor functions over time.