AQA GCSE Biology - The Nervous System and Homeostasis

Homeostasis: Homeostasis is a process by which your body maintains a constant internal temperature. Internal conditions controlled include:

• water content
• temperature
• glucose concentration

It is important for our body to respond to these changes as our body has an optimum at which it works at. i.e. if our body’s temperature is too high and this isn’t regulated, our enzymes would denature, slowing our metabolism.

Receptor Cells: Detect the stimulus

Coordination Centers: eg: the brain, spinal cord, pancreas

Effectors: Muscles of glands which bring about the response

[[The Nervous System[[

The nervous system is comprised of receptors, nerves, the central nervous system (CNS) and effectors.

Neuron: A neuron is a specialized cell. it has a long body in order to send signals faster. it also has dendrites and nerve endings.

==A nerve is multiple neurons==

Central Nervous System (CNS): Made up of brain and spinal cord

Stimulus →Receptor →Sensory Neuron →CNS →Motor Neuron → Effector (Muscle/Gland) → Response

Homeostasis: Maintenance of constant internal conditions

Relay Neurons: Carry electrical impulse from one part of CNS to another

Nerve: Multiple neurons

Sensory Neuron: Carry electrical impulse from Receptor to CNS

Coordinator: Brain or spine; coordinates response

Peripheral Nerves: All nerves EXCEPT brain and spine

Motor Neuron: Transmits impulse from CNS to body tissues

Stimulus: Change in environment body reacts to

Effector: Muscle or gland that reacts to nerve impulse

Receptor Cells: Specialist cells that detect impulse

[[Reflex Arc[[

Synapse: Gap between two neurons

Events across Synapse

• Pre-synaptic neuron contains vesicle containing neurotransmitters
• Electrical impulse arrives at end of neuron. This stimulates the vesicles to move towards and fuse with the membrane
• Neurotransmitters diffuse across the synapse form an area of high concentration to an area of low concentration (down the concentration gradient)
• Neurotransmitter binds to the receptor on the surface of the post-synaptic neuron

[[The Brain[[

Cerebrum:

• largest part of brain
• memories, consciousness, intelligence, language

Cerebellum:

• below cerebrum, at the back
• coordination and control of muscles

Medulla:

• top of spine, more primitive
• unconscious activities, i.e breathing

[[The Eye[[

Sclera: tough, white, outer layer - protects eye

Cornea: transparent area in front of sclera ; can bend light as it enters

Suspensory Ligament: holds lens in place

Pupil: hole through which light enters

Fovea: area of cones where light is bought to focus

Optic Nerve: sends electrical signal to the brain

Iris: controls the size of the pupil

Lens: clear disc - can change shape to focus light on retina

Ciliary Muscle: contracts and relaxes to change the shape of the lens

Retina: layer at back containing light sensitive cells - rods and cones

Circular v Radial Muscles

==Circular Muscles -== contract to bring iris further in, opening pupil

==Radial Muscles -== contract to dilate pupil by pushing pupil further out.

How the Eye Works

• Ciliary muscles change the shape of the lens, which alters the refraction of light. This means light is always focused on the retina - called accommodation
• Light hits the retina and stimulates the rods and cones
• They send impulses to the brain via the optic nerve
• Image in the retina is upside down - the brain corrects this
• There is a blind spot where the optic nerve leaves the eye

Close Objects

• ciliary muscles contracts
• suspensory ligament looses
• lens is thicker; refracts more light

Distant Objects

• ciliary muscles relax
• suspensory ligament tightens
• lens is pulled thin; little light refracted

What Happens to Lenses as we Age?

Your lens starts to harden and takes longer to change shape, making it difficult to focus on objects. As light is no longer focused on the retina, you can develop myopia or hyperopia.

Myopia: Short-sightedness

• close objects are in focus - distance looks blurred
• use concave lens - spreads light out before it reaches the eye

Hyperopia: Long-sightedness

• objects in distance are in focus - closer objects look blurred
• use convex lens - brings light rays together before it reaches the eye

Contact lenses: Float on the surface of the cornea, focusing and refracting light

LASIK: Reshapes the cornea surgically - common for myopia

[[Thermoregulation[[

Negative Feedback: Make adjustments to bring body back to bodily norm

Internal environment normal → Internal environment changes → detector sense change → Body makes adjustments → Internal environment returns to norm

The Thermoregulatory Center (specifically, the Hypothalamus) detects and controls your body’s internal temperature. It receives impulses from the skin receptors and blood flowing through the hypothalamus.

Too Hot

• hairs lay flat
• vasodilation - arterioles dilate, increasing blood flow to surface of skin →more heat lost through radiation
• increased sweating → heat lost through evaporation

Too Cold

• shivering - muscles contract and relax rapidly with energy from respiration →respiration is exothermic and releases heat
• hairs stand up
• vasoconstriction → reduces heat loss through radiation
• decreased sweating