human bio year 12 (3)

Nervous System Overview

Functions of the Parts of the Brain and Spinal Cord

Cerebral Cortex

  • Involved in higher order functions such as:

    • Thinking

    • Learning and reasoning

    • Intelligence

    • Memory

    • Perception of the senses

    • Sense of responsibility

Medulla Oblongata

  • Regulates vital functions:

    • Cardiac Center: Controls heart rate and force of contraction

    • Vasomotor Center: Regulates diameter of blood vessels

    • Respiratory Center: Controls rate and depth of breathing

  • Participates in reflex actions such as sneezing and coughing

Hypothalamus

  • Maintains homeostasis in the body:

    • Controls endocrine functions

    • Regulates body fluids and temperature

    • Involved in emotional responses

    • Regulates waking and sleeping patterns

Cerebellum

  • Coordinates movement, posture and balance

  • Fine motor movement control

Corpus Callosum

  • Connects the left and right hemispheres of the brain

Pons

  • Connects various parts of the brain

  • Involved in the perception of sight

Spinal Cord

  • Integrates reflex control

  • Relays messages between the brain and peripheral nervous system

  • Composed of:

    • White matter (surrounding)

    • Grey matter (inner core)

Divisions of the Nervous System

Central Nervous System (CNS)

  • Comprises the brain and spinal cord

Peripheral Nervous System (PNS)

  • Comprises nerves that transmit messages to and from the CNS

Protection of the CNS

  • Bone:

    • Skull (cranium) protects the brain

    • Vertebral canal protects the spinal cord

Meninges

  • Three protective tissue layers covering the CNS:

    • Dura Mater: Tough outer layer

    • Arachnoid: Loose middle layer, vascular

    • Pia Mater: Delicate inner layer, adheres to the brain and spinal cord; forms blood-brain barrier

Cerebrospinal Fluid (CSF)

  • Functions of CSF:

    • Acts as a shock absorber

    • Supports brain flotation

    • Circulates between layers and through brain cavities

    • Takes nutrients to and removes waste from neuronal cells

Neurons

Structure and Function

  • Basic structural and functional units of the nervous system

  • Composed of a cell body, dendrites, and axons:

    • Dendrites: Short extensions carrying impulses towards the cell body

    • Axon: Long extension carrying impulses away from the cell body, usually covered by a myelin sheath

Types of Neurons

  1. Sensory Neurons: Carry messages to the CNS

  2. Motor Neurons: Carry messages from the CNS to muscles and glands

  3. Interneurons: Connect sensory and motor neurons within the CNS

Transmission of Nerve Impulses

Resting Membrane Potential

  • Maintained at -70mV; inside negative, outside positive

Action Potential

  • Occurs in response to stimuli greater than threshold potential (15 mV):

    1. Depolarization: Reversal of charges during action

    2. Repolarization: Restores resting state

    3. Hyperpolarization: Membrane potential temporarily becomes more negative

  • Refractory period prevents backflow of nerve impulses

Speed of Nerve Impulses

  • Myelinated fibers conduct faster (up to 140 m/s) via saltatory conduction

Synaptic Transmission of Nerve Impulses

  1. Action potential reaches the axon terminal

  2. Voltage-gated K+ and Ca2+ channels open

  3. Neurotransmitters released via exocytosis into the synapse

  4. Bind to receptors on the post-synaptic neuron, generating a response

Neurotransmitters

  • Examples: Acetylcholine

  • Effects of Neurotoxins: May block receptors preventing normal signaling leading to paralysis

Endocrine System

Classification of Glands

  • Exocrine Glands: Secrete substances via ducts (e.g., sweat glands)

  • Endocrine Glands: Secrete hormones directly into the bloodstream (e.g., pituitary gland)

Functions of the Endocrine System

  1. Maintain homeostasis in body fluids

  2. Response to stress

  3. Regulation of growth and reproduction

Key Endocrine Glands

Hypothalamus

  • Links nervous and endocrine systems; regulates multiple body functions

Pituitary Gland

  • Anterior Lobe: Connected via blood vessels, releases numerous important hormones (e.g., FSH, LH)

  • Posterior Lobe: Connected via nerve fibers, releases hormones made in the hypothalamus

Hormonal Actions

  • Hormones act on specific target cells to produce biological effects e.g., growth, metabolism regulation

Feedback Mechanisms in Homeostasis

Definition of Homeostasis

  • Maintenance of a constant internal environment

Negative Feedback

  • Response counteracts the stimulus (e.g., temperature regulation)

Positive Feedback

  • Response amplifies the initial stimulus, often leading to a greater effect (e.g., childbirth)

Immune System Overview

Pathogens

  • Disease-causing organisms include bacteria, viruses, fungi, and parasites

Defense Mechanisms

  • External Defenses: Skin, mucous membranes, acids, and flushing actions like tears and sweat

  • Internal Non-Specific Defenses: Include phagocytes (like macrophages) and inflammatory responses

Evolution through Natural Selection

Major Concepts

  1. Variation within populations

  2. Overproduction of offspring leading to competition for resources

  3. Favorable traits promote better survival and reproductive success; these traits get passed down

Mutation and Genetic Variation

Definitions

  • Mutations: Permanent structural alterations in DNA that can increase genetic variation within populations

  • Gene Pool: Sum of all alleles in a population; allele frequency describes how often each allele appears in the pool

Effects of Mutations

  • Beneficial mutations can improve survival rates and be passed through generations, leading to evolution

Evidence for Evolution

Fossils

  • Fossils provide insight into past life forms and biological changes over time

Comparative Anatomy and Embryology

  • Studying anatomical similarities and embryonic development among species reinforces common ancestry

Conclusion

  • The nervous and endocrine systems collaborate to maintain homeostasis, responding dynamically to both internal and external stimuli.