Year 9 Biology: Chapter 1.5 - The Nervous System

Year 9 Biology: Chapter 1.5 - The Nervous System

Overview of the Nervous System

  • The nervous system allows for various involuntary and voluntary actions including:

    • Movement

    • Digestion

    • Breathing

    • Thinking

    • Talking

    • Pumping blood around the body

  • It operates alongside the endocrine system to detect issues and control bodily functions and responses.

Structure of Nerves

  • Nerve cells, also known as neurons, are:

    • The longest cells in the body.

    • Responsible for transmitting electrical impulses in one direction.

  • Neurons bundle together to form nerves, which are wrapped in a protective sheath.

Neuronal Structure and Function

  • Myelin Sheath: Neurons are covered with a layer called the myelin sheath which:

    • Electrically insulates neurons from each other.

    • Increases the speed of nerve impulse transmission.

Types of Neurons

  1. Sensory Neurons:

    • Detect stimuli from external or internal environments through receptors located at the axon terminal.

    • Transmit nerve impulses to the brain or spinal cord via synapses at dendrites.

  2. Motor Neurons:

    • Receive messages from the brain that are sent to muscles or glands.

    • Facilitate movement and the release of hormones.

Sensory Neurons and Their Functions

  • **Stimuli and Corresponding Receptors:

    • Light → Rods and cones in the eye

    • Sound → Cells in the inner ear

    • Touch, pain, heat, vibration, pressure → Skin receptors

    • Chemicals in food → Taste buds on the tongue

    • Chemicals in air → Olfactory cells in the nose**

Differences Between Sensory and Motor Neurons

  • Sensory Neurons:

    • Carry messages from sense organs (eyes, ears, tongue, skin) to the brain and spinal cord (CNS).

  • Motor Neurons:

    • Communicate messages from the CNS to effectors (muscles or glands) that execute responses.

Communication Across Synapses

  • Nerve Impulses at Synapses:

    • At synapses, electrical signals convert into chemical signals (neurotransmitters) and then back to electrical signals to facilitate communication between neurons.

Myelin and Neural Tissue

  • Myelin:

    • Appears white and is responsible for forming white matter.

    • Gray Matter: Does not contain myelin and is associated with processing and signaling in the brain and spinal cord.

The Nervous System Components

  • Central Nervous System (CNS):

    • Comprises the brain and spinal cord.

  • Peripheral Nervous System (PNS):

    • Comprises all other nerves, including cranial and spinal nerves.

Spinal Cord Segmental Functions

  • Cervical Segments:

    • C1-C3: Neck muscles

    • C4: Diaphragm

    • C5: Deltoid (shoulder)

    • C6: Wrist

    • C7: Triceps

    • C7-C8: Fingers

    • T1: Hand & Thoracic movements

    • T7-L1: Intercostals (trunk musculature)

    • T11-L2: Ejaculation

    • L2: Hips

    • L3: Quadriceps

    • L4-L5: Hamstrings, Knee

    • L4-S1: Foot movement

    • S2: Penile erection

    • S2-S3: Bowel and bladder control.

Spinal Cord Structure

  • Composed of:

    • Spinal nerves, which convey sensory and motor pathways.

    • Divided into sensory (posterior) and motor (anterior) roots.

The Brain: Overview

  • Serves as the control center for the nervous and endocrine systems.

  • Connected to all body parts and is enclosed by the skull for protection.

Major Parts of the Brain

  • Cerebrum: The largest brain part responsible for:

    • Personality

    • Voluntary actions including memory, speech, and conscious thought.

  • Cerebellum: Coordinates involuntary activities including balance and muscle coordination.

  • Brain Stem: Controls vital involuntary actions such as heartbeat, digestion, and breathing.

Hemispheres of the Brain

  • The brain consists of left and right hemispheres which:

    • Collaborate on most activities.

    • Certain functions are localized, thus debunking the myth of being strictly 'left-brained' or 'right-brained'.

Lobes of the Brain

  • Frontal Lobe:

    • Involved in reasoning, problem-solving, emotions, and personality.

    • Associated with long-term memory.

Frontal Lobotomy

  • Procedure historically used (1930s-1950s) to reduce mental distress:

    • Involves severing connections between the frontal lobe and other brain parts.

    • Now used in extreme cases due to significant side effects.

Phineas Gage Case Study

  • Background:

    • American railroad foreman who survived a severe brain injury (iron rod through left frontal lobe).

    • Remarkably returned to normal functions (walking, talking).

    • Experienced a drastic change in personality.

Other Brain Lobes and Their Functions

  • Parietal Lobe:

    • Processes senses, numbers, and object manipulation.

  • Occipital Lobe:

    • Center of vision processing.

  • Temporal Lobe:

    • Handles language, hearing, and speech, as well as long-term memory.

Cerebellum Functionality

  • Roles of the Cerebellum:

    • Controls involuntary muscle coordination and maintaining balance.

Conclusion on Brain Structure

  • The brain has a complex structure with specialized regions that contribute to various bodily functions. Each lobe and part works collectively to maintain homeostasis and facilitate communication between different body systems.