Year 9 Biology Notes: The Nervous System

The Central Nervous System

The Nervous System

• The nervous system is a communication system controlling all parts of the body.
• The human nervous system has two main parts:
  • Central Nervous System (CNS): Brain and spinal cord.
  • Peripheral Nervous System (PNS): Nerves in limbs and organs.
• Role of the nervous system: Communication and control.
• Two main divisions: Central Nervous System (CNS) and Peripheral Nervous System (PNS).
• Information flow: Touch receptors in toes send info to the brain.

Central Nervous System (CNS)

• The CNS is the control center of the body.
• Consists of the brain and spinal cord.
• Functions:
  1. Receives information from the body.
  2. Processes information.
  3. Sends messages for responses.
• Structures of the CNS: Brain and spinal cord.
• Function of the CNS: Information processing and response initiation.

Protection of the Central Nervous System

• The CNS interprets information and initiates responses, requiring careful protection.
• Protective structures:
  • Skull: Protects the brain.
  • Vertebral column (spine): Protects the spinal cord.
  • Muscles
  • Cerebral fluid
  • Meninges
• Importance of protection: The brain and spinal cord are vital for bodily functions.

The Brain

• The brain processes internal and external information.
• It makes decisions about movements and internal changes.
• Processes thoughts, memories, and emotions.
• Protection: Skull.
• Function of the brain: Information processing, decision making, and control.

The Spinal Cord

• Long, thin bundle of nerves.
• Connects the brain to the rest of the body.
• Function: Carries sensory and motor messages between the brain and the body.
• Protection: Vertebral column.
• Function of the spinal cord: Message transmission between brain and body.

Neurons and Meninges

• Neurons: Basic unit of the nervous system, carry messages.
• Types of neurons: Sensory, motor, interneurons.
• Meninges: Three membranes that protect the brain and spinal cord.
• Function of neurons: Carry messages throughout the nervous system.

The Brain (Detailed)

• Three main parts of the brain:
  • Cerebrum
  • Cerebellum
  • Brain stem
• The cerebrum contains four lobes:
  • Frontal lobe
  • Temporal lobe
  • Parietal lobe
  • Occipital lobe
• Three main parts of the brain: Cerebrum, Cerebellum, Brain stem.
• Number of lobes in the cerebellum: The transcript has an error. It should refer to the cerebrum, not the cerebellum. The cerebrum has four lobes.

The Brain – Frontal Lobe

• Location: Front of the brain.
• Functions: Reasoning, emotions, movement, problem-solving.
• Side effects of damage: Impaired reasoning, emotional instability, movement difficulties.

The Brain – Temporal Lobe

• Location: Sides of the brain.
• Functions: Interpreting, organizing, and remembering information, understanding language, processing smells/sounds, and recognizing faces.
• Senses without temporal lobe input: The temporal lobe receives information from almost all senses except vision. This highlights its broad role in sensory processing and memory.

The Brain – Parietal Lobe

• Location: Top of the brain.
• Functions: Perception of taste, pain, temperature, and touch; spatial awareness.
• Sensory organs sending information: Skin and tongue.
• Spatial awareness provides a sense of where your body is and how it relates to the outside world.

The Brain – Occipital Lobe

• Location: Back of the brain.
• Functions: Perception of vision, including distance, depth, location, and object identity.
• Effect of hitting the back of the head: Potential vision impairment or temporary blindness due to disruption of visual processing in the occipital lobe.

The Brain – Cerebellum

• Location: Base of the cerebrum.
• Functions: Controls coordination and balance.
• Without it: Standing and walking would be impossible.
• Responsibility of cerebellum: Coordination and balance.

The Brain – Brain Stem

• Location: Base of the brain, connects to the spinal cord.
• Functions: Controls vital functions such as breathing, blood pressure, and heart rate.
• Connection: Connects to the spinal cord.
• Voluntary control: No, vital functions are involuntary.

The Spinal Cord

• Links the brain and the nerves of the Peripheral Nervous System.
• Protected by the bones of the spinal column (vertebrae).
• Bones of the spine: Vertebrae.
• Effect of spine damage: Disconnection of signal transmission.

The Peripheral Nervous System (PNS)

• Central Nervous System: Brain and spinal cord.
• Peripheral Nervous System: Nerves in the limbs and organs.
• Divisions of the PNS:
  • Somatic Nervous System
  • Autonomic Nervous System
• Difference between CNS and PNS: Structure and location.
• Two parts of the PNS: Somatic and Autonomic Nervous Systems.

Somatic Nervous System (SNS)

• Collects information from receptors in sense organs.
• Coordinates body movement in response (voluntary muscle movements).
• Example: Taking off a jumper in hot weather.
• Controls voluntary muscle movements.
• Stimuli include temperature, light, touch, smell, and sound.

Autonomic Nervous System (ANS)

• Controls involuntary actions of the body.
• Actions include heartbeat, digestion, respiration, salivation, pupil size, and perspiration.
• Maintaining the body’s internal environment.
• Controls involuntary actions.
• Involuntary: Done without conscious control.
• Perspiration: The process of sweating

Neurons

• The nervous system consists of trillions of neurons (nerve cells).
• Carry electrical messages (nerve impulses) at high speed.
• Nerve impulses travel in one direction only.
• Another name for neurons: Nerve cells.
• Nerve impulses: Electrical messages.

Neuron Structure

• Five main parts:
  • Cell body (with nucleus)
  • Dendrites
  • Axon
  • Synaptic terminals
  • Myelin sheath
• Nucleus location: Cell body.
• Path of a nerve impulse: Dendrites to cell body to axon to synaptic terminals.
• Without myelin sheath: Slower nerve impulse transmission.

Types of Neurons

• Sensory neurons: Carry messages towards the brain (CNS).
• Motor neurons: Carry messages away from the brain (CNS).
• Interneurons: Link sensory and motor neurons.
• Difference between sensory and motor neurons: Direction of message.
• Role of an interneuron: Connect sensory and motor neurons.

Sensory Neurons

• Receptors are sensory neurons (afferent neurons).
• Cell body hangs off its axon, without dendrites.
• Location: Sensory organs.
• Sensory neuron's cell body is not surrounded by dendrites.
• Function: Detect stimuli and send information to the brain.
• Receptor: Detects stimuli and sends information to the brain.
• Stimulus: Causes part of the body to respond.

Motor Neurons

• Motor neurons (efferent neurons) carry messages from the brain and spinal cord to muscles and glands.
• Motor neurons cause an effect via movement (motor means movement): EFFECT has the same first four letters as EFFErent.
• Destination: Muscles and glands.
• Motor neurons connected to the stomach: Yes, for controlling digestive processes.

Interneurons

• Interneurons (relay or connector neurons) link sensory neurons and motor neurons or other interneurons.
• Located in the central nervous system (brain and spinal cord).
• Usually do not need a myelin sheath.
• Connections: Sensory neurons, motor neurons, and other interneurons.
• Identification: Location within the CNS (brain and spinal cord).

Synapses

• Information flows across a gap called a synapse.
• Neurotransmitters carry the nerve impulse to the next neuron.
• Some synapses allow direct electrical transmission.
• Synapse: The gap between neurons where information is transmitted.
• Neurotransmitters: Chemicals that transmit nerve impulses across synapses.

Reflexes

• Reflex action: Involuntary, rapid response to a stimulus.
• Voluntary response: Conscious response to a stimulus.

Reflex Arc

• Neural pathways act on an impulse before it reaches the brain.
• Faster actions prevent injury and protect the body.
• Message sent:
  • To the brain for processing.
  • Immediately to the motor neuron and muscles for reaction.
• Locations: Spinal cord and brain.
• Reflex actions are faster because the impulse is acted on prior to it reaching the brain.

Grasp Reflex

• Stimulus: Object touching the palm.
• Receptor: Mechanoreceptors in the skin.
• Control center: Spinal cord.
• Response: Curling the fingers.

Knee-Jerk Reflex

• Stimulus: Tapping below the kneecap.
• Receptor: Mechanoreceptors in the skin.
• Control center: Spinal cord.
• Response: Kicking the foot.

Homeostasis

• Homeostasis: Maintaining stable internal conditions.
• Internal conditions regulated:
  1. Temperature
  2. Water and salt content
  3. Available blood sugar
  4. Available oxygen
  5. Concentration of wastes in the blood.
• Regulation: Coordination of organs using the nervous system and the endocrine system.
• Coordination during homeostasis: Various organs, including the nervous and endocrine systems.
• Homeo = same; Stasis = stable; Regulation = control or maintain.
• Homeostasis: The process of keeping internal conditions stable and at a healthy range.

Negative Feedback Loop

• Involves:
  1. Receptors (sensor) that are sensitive to a particular stimulus.
  2. A control that sends messages to the effectors.
  3. Effectors create a response stimulus. If the stimulus is supressed, then it is a Negative Feedback Loop.
• Receptors detect the stimulus.
• Outcome of negative feedback: Suppressed stimulus
• Homeo = same; Stasis = stable; Regulation = control or maintain

Air Con Example (Negative Feedback)

• Air conditioner responds to suppress the temperature stimulus.
• If the temperature drops below the optimal range, the air conditioner will turn off in cooling mode or switch to heating mode.

Thermoregulation in Humans (Negative Feedback)

• Heating mechanisms activated (shivering).
• Cooling mechanisms activated (sweating).
• $Body \,temperature \,decreases \,+ \,Body \,temperature \,increases$
• $Body \,temperature \,increases \,+ \,Body \,temperature \,decreases$

Body Temperature (Negative Feedback)

• Normal body temperature: Around 37°C.
• Response to increased body temperature: Sweating, blood flow to the skin, behavior change.
• Behavioural changes to decreased body temperature: Putting on a jumper.
  TOO HOT (above 37) TOO COLD (below 37)
• Behaviour change (taking off jumper). Behaviour change (putting on jumper)
• Blood flow is sent to the skin Blood flow is diverted from skin
• Sweating (perspiration) evaporates water on the skin. Goose bumps on the skin trap warm air.
• Decrease body temperature Increase Body Temperature
• Change in temperature: Detected by thermoreceptors.
• Effector of an increase in temperature: Sweat glands.

Feedback loop for decreased temperature: Increased shivering to generate heat.
Effectors of decreased temperature: Muscles shivering, blood diverted from the skin.

The Endocrine System

• Endocrine system: Network of glands that release hormones.
• Hormones: Chemical messengers that travel through the blood.
• Endocrine system definition: Network of glands releasing hormones.
• Hormones travel: Through the bloodstream.

How Hormones Work

• Hormones are protein chemical messengers that maintain control (and growth) of the body.
  1. Travelling through the blood.
  2. Finding a target cell with a specific receptor.
  3. Making the target cell change what it is doing.
• Hormones Definition: Chemical messengers.
• Target cells Definition: Cells with specific receptors for hormones.

Target Cells

• Hormone specificity: Shape fits target cell receptor (like a lock and key).
• Activity Initiation: Only one hormone needed to cause change.
• Hormones are specific because: Their shape only fits one target cell.

Endocrine Gland Locations

• Endocrine glands: Release hormones directly into the bloodstream.
• Hypothalamus and pituitary gland location: Brain.
• Other endocrine glands: Thyroid, adrenal glands, pancreas, ovaries, testes, pineal gland.

Endocrine Control

• Pituitary gland: Master gland, controlled by the hypothalamus.
• Hypothalamus role: Links the nervous and endocrine systems, monitors body environment and controls hormone release via the pituitary gland.
• Pituitary Gland Called the ‘master gland’ that is under the hypothalamus. It controls other glands by sending hormones to them.

Why is the pituitary gland called the master gland? It controls other glands.
What is the role of the hypothalamus? Links the nervous and endocrine systems

Endocrine Glands and Their Functions

Responding to Stimuli

• Stimuli: Information the body receives that causes a physiological or behavioral response (external or internal).
• Stimulus: Any information that the body receives causing a response.
• Examples of environmental changes: Hot day, loud noise.
• Examples of internal changes: Low blood sugar, dehydration.

Receptors

• Receptor: Detects a stimulus or change and sends information to the brain.
• Example: Tastebuds detect tastes.
• Relationship between stimuli and receptors: Receptors detect changes in the environment which are called stimuli.

Sense Organs

• Five main senses: Sight, hearing, taste, smell, touch.
• Sense organs: Eyes, ears, tongue, nose, and skin.
• Five sense organs: eyes, ears, tongue, nose, and skin
• Stimulus for the nose: Odors in the air.
• Sense organs detect external stimuli.

Sight

• Sight: Photoreceptor cells transform light into nerve signals for the brain.
• Process: Photoreceptor transform light into nerve signals for the brain which interprets this information.
• Example where eyes resond: Sunlight.

Hearing

• Hearing: Sounds cause vibrations which makes the eardrum vibrate, sending information through mechanoreceptors to the brain.
• Vibrations of air particles causes the eardrum to vibrate.
• Situation where ears respond: Loud concert.

Taste

• Taste: Taste buds contain chemoreceptor cells reacting to chemicals in food and can recognise sweet, salty, sour, and bitter tastes.
• Brain recognizes what is being eaten, when information from the taste buds is transferred to the brain.
• Example situation that our tastebuds would respond to: Eating chocolate.

Smell

• Smell: Nostrils contain chemoreceptors detecting chemicals in the air while the receptors send signals to the brain to interpret what we are smelling.
• Chemical receptors in the nose detect chemicals in the air and send signals to the brain.
• Smell and taste are linked because they both use chemoreceptors to detect environmental signals.

Touch

• Touch: Dermis contain different receptors that detect pressure and pain (mechanoreceptors) and warm and cold sensations. Skin signals are sent from receptors to the brain for interpretation and processing.
• Touch receptors detect pressure and pain.
• Two situations for pressure response: Hug and stubbing toe.