the nervous system 🧠
Think of your body as a house.
Brain = the boss who makes decisions.
Spinal cord = the main communication cable.
Nerves = the smaller cables that carry messages around your body.
The nervous system helps you think, feel, move, and react to things.
1. The two main divisions
CNS — Central Nervous System
Brain + spinal cord
The control centre. It processes information and coordinates responses.
PNS — Peripheral Nervous System
Nerves outside the brain and spinal cord
Carries messages between the CNS and the rest of the body.
2. Sensory vs motor nerves
Imagine touching a hot kettle.
Sensory (afferent) neurons
Carry information TO the CNS. Your hand senses heat and sends a message to your spinal cord and brain.
Motor (efferent) neurons
Carry commands AWAY from the CNS to muscles or glands. Your muscles contract to move your hand.
3. Voluntary vs involuntary
Voluntary: You consciously choose the action, like lifting your arm.
Involuntary: Happens without conscious control, like your heart beating.
Reflex: A rapid, automatic response, like pulling your hand away from something hot.
The brain & meninges
1. The 3 main parts of the brain
Think of your brain as having three main jobs.
1. Cerebrum — THINK 🧠
Thinking, memory and intelligence
Interpreting your senses
Voluntary movements
Memory trick: Cerebrum = clever brain.
2. Cerebellum — BALANCE 🤸
Balance and posture
Coordination of movements
Helps movements become smooth and accurate
Memory trick: CEREBELLUM = BALANCE.
3. Brainstem — SURVIVE ❤
Helps regulate breathing
Helps regulate heart rate
Controls important automatic functions
Memory trick: Brainstem = basic life functions.
2. The meninges — 3 protective layers
The meninges are three membranes that surround and protect the brain and spinal cord.
Learn them from the outside going inward.
1 Dura mater — DURABLE
The tough, outermost layer.
2 Arachnoid mater — WEB
The middle layer, with a web-like appearance.
3 Pia mater — PRETTY CLOSE
The delicate inner layer that closely follows the brain's surface.
Learn them from the outside going inward.
1 Dura mater — DURABLE
The tough, outermost layer.
2 Arachnoid mater — WEB
The middle layer, with a web-like appearance.
3 Pia mater — PRETTY CLOSE
The delicate inner layer that closely follows the brain's surface.
Neurotransmitters
1. What is a neurotransmitter?
A neurotransmitter is a chemical messenger that carries a signal from one nerve cell to another, or to another target cell.
Imagine two nerve cells with a tiny gap between them. The neurotransmitter carries the message across that gap.
Remember the sequence:
1. Electrical signal reaches nerve ending
2. Chemical messenger is released
3. Messenger binds to receptors on the next cell
2. The important neurotransmitters
1. Acetylcholine (ACh) — ACTION 💪
Helps muscles contract. Also important for learning, memory and attention.
Memory trick: ACh = Action!
2. Dopamine — DRIVE 🏆
Involved in motivation, reward, learning and movement.
Memory trick: Dopamine = Drive and reward.
3. Serotonin — STATE OF MOOD 😊
Helps regulate mood, sleep and appetite.
Memory trick: Serotonin = State of mood.
4. Noradrenaline — ALERT 👀
Helps with alertness, attention and the body's response to stress.
Memory trick: Noradrenaline = Notice everything!
5. Adrenaline — ALARM 🚨
Prepares your body for fight-or-flight by increasing heart rate and readiness for action. It acts mainly as a hormone in the bloodstream, although it can also act as a neurotransmitter.
Memory trick: Adrenaline = Alarm mode!
3. Two extra ones to know
Neurotransmitter Main function Memory trick
GABA Main inhibitory neurotransmitter in the brain; reduces neuronal activity GABA = brake
Glutamate Main excitatory neurotransmitter in the brain; important for learning and memory Glutamate = go
The endocrine system
1. What is the endocrine system?
The endocrine system is a group of glands that release hormones to control and coordinate activities in your body.
Think of it like your body's messaging service 📱
Glands = the factories.
Hormones = the messages.
Bloodstream = the delivery service.
Target organs = the places receiving the messages.
For example, when your blood sugar rises after eating, your pancreas releases insulin to help bring it down.
2. The BIG difference: endocrine vs exocrine
This is a favourite type of anatomy test question, so learn this!
ENDOCRINE = NO DUCTS 🩸
Releases hormones into the bloodstream.
Examples: thyroid gland, pituitary gland and adrenal glands.
EXOCRINE = DUCTS 🚰
Releases substances through ducts onto a surface or into a body cavity.
Examples: sweat glands, salivary glands and sebaceous (oil) glands.
Memory trick: Endocrine = enters the blood. Exocrine = exits through a duct.
What about the pancreas?
The pancreas does BOTH jobs!
Endocrine: releases insulin and glucagon into the blood.
Exocrine: releases digestive enzymes through a duct into the small intestine.
Remember this one because it's a great exam example.
3. Important endocrine glands
Don't memorise every hormone at once. Start with the gland and its main job.
1. Pituitary gland — THE CONTROLLER
Produces hormones that regulate several other endocrine glands. It is controlled by the hypothalamus.
Memory trick: Pituitary = powerful little gland.
2. Thyroid gland — METABOLISM 🔥
Produces thyroid hormones that help regulate metabolic rate, energy use and growth.
3. Adrenal glands — STRESS 🚨
Produce hormones including adrenaline and cortisol, which help the body respond to stress.
4. Pancreas — BLOOD SUGAR 🍬
Insulin lowers blood glucose.
Glucagon raises blood glucose.
5. Gonads — REPRODUCTION
Ovaries produce oestrogen and progesterone.
Testes produce testosterone.
These hormones are important for reproduction and sexual development.
4. What is a hormone?
A hormone is a chemical messenger released by an endocrine gland that travels through the blood to affect target cells.
Here's the difference between what we learned earlier and today:
Neurotransmitter Hormone
Usually carries a signal across a synapse Often travels through the bloodstream
Usually acts over a very short distance Can reach distant target organs
Example: acetylcholine Example: insulin
Muscles & muscle movements
1. The 3 types of muscle
1. Skeletal muscle 💪
Attached to bones.
Usually under voluntary control.
Helps you walk, write and lift things.
Memory trick: Skeletal = skeleton.
2. Cardiac muscle ❤
Found in the heart.
Involuntary.
Contracts rhythmically to pump blood.
Memory trick: Cardiac = cardiac (heart).
3. Smooth muscle 🍽
Found in organs such as the intestines and blood vessels.
Involuntary.
Moves substances through organs and helps regulate the diameter of blood vessels.
Memory trick: Smooth = inside organs.
shortcut:
Muscle Location Control
Skeletal Attached to bones Usually voluntary
Cardiac Heart Involuntary
Smooth Walls of organs Involuntary
2. The muscle movements you MUST know
Flexion = BEND
Decreases the angle at a joint.
Example: bending your elbow to bring your hand toward your shoulder.
Extension = STRAIGHTEN
Increases the angle at a joint.
Example: straightening your elbow.
Abduction = AWAY
Moves a body part away from the body's midline.
Example: lifting your arm sideways away from your body.
Adduction = ADD
Moves a body part toward the body's midline.
Example: bringing your arm back down to your side.
Pronation vs supination
Pronation = turning your forearm so your palm faces down.
Supination = turning your forearm so your palm faces up.
Other movement terms worth knowing:
Rotation: turning around an axis, like turning your head.
Circumduction: moving a limb in a circular, cone-shaped pattern.
Dorsiflexion: lifting your toes toward your shin.
Plantar flexion: pointing your toes downward, like standing on tiptoes.
3. Muscle names from your notes
Let's learn these by where they are and what they do rather than memorising a random list.
Abdominal muscles — your core
Rectus abdominis: bends the trunk forward.
External and internal obliques: help rotate and bend the trunk sideways.
Transversus abdominis: compresses the abdominal contents and helps stabilise the trunk.
Memory trick: Rectus = straight-up abs.
Front of thigh — quadriceps
The quadriceps femoris group contains four muscles and extends (straightens) the knee.
Memory trick: Quads = four; front thigh = straighten knee.
Back of thigh — hamstrings
Biceps femoris
Semitendinosus
Semimembranosus
They bend the knee and help extend the hip.
Memory trick: Hamstrings = back thigh, bend knee.
Back of lower leg — calf muscles
Gastrocnemius: helps point the foot downward and bend the knee.
Soleus: helps point the foot downward.
Calcaneal (Achilles) tendon: connects the calf muscles to the heel bone.
Memory trick: Calf muscles = tiptoe power.
Upper arm — biceps and triceps
Biceps brachii: helps bend the elbow.
Triceps brachii: straightens the elbow.
Memory trick: Biceps bends; triceps straightens.
4. How muscles work together
Muscles often work in antagonistic pairs. This means one muscle produces a movement while its opposing muscle produces the opposite movement.
For example, when you bend your elbow:
The biceps contracts to help bend it.
The triceps relaxes as the opposing muscle.
When you straighten your elbow, the triceps contracts to extend it.
Important: Muscles pull when they contract; they don't actively push bones.
Spinal nerves
1. What are spinal nerves?
Spinal nerves are nerves that connect the spinal cord to the rest of the body. They carry sensory information to the central nervous system and motor commands away from it.
Think of your spinal cord as a main electrical cable and your spinal nerves as smaller cables branching out to your muscles, skin and organs.
2. The magic number: 31 pairs!
You have 31 pairs of spinal nerves — one pair on each side of the spinal cord at each spinal level.
8
Cervical (C1–C8)
Neck; nerves also supply the diaphragm and upper limbs.
12 Thoracic (T1–T12)
Chest and much of the abdominal wall.
5
Lumbar (L1–L5)
Lower back and parts of the lower limbs.
5
Sacral (S1–S5)
Pelvis, pelvic floor and parts of the lower limbs.
1 Coccygeal (Co1)
The small region around the tailbone.
3. The two spinal nerve roots
This is VERY important for understanding how messages travel.
🔵 Dorsal root = SENSORY IN
Carries sensory information toward the spinal cord.
Example: feeling a pinprick on your finger.
🔴 Ventral root = MOTOR OUT
Carries motor commands away from the spinal cord.
Example: sending a command to move your finger.
Memory trick: DAVE!
Dorsal = Afferent = sensory information arriving.
Ventral = Efferent = motor information exiting.
A spinal nerve forms when the dorsal and ventral roots join. The spinal nerve is therefore a mixed nerve, containing both sensory and motor fibres.
4. What is a reflex arc?
A reflex is a quick, automatic response to a stimulus.
Imagine touching something painfully hot:
1. Receptor
Your skin detects the stimulus.
2. Sensory neuron
Carries the signal to the spinal cord.
3. Integration centre
The spinal cord processes the reflex signal.
4. Motor neuron
Carries the command to the muscle.
5. Effector
The muscle contracts and pulls your hand away.
Exam tip: A withdrawal reflex can be coordinated by the spinal cord before the brain consciously processes the pain.
The autonomic nervous system
1. What is it?
The autonomic nervous system (ANS) controls many automatic body functions that happen without you consciously thinking about them.
Examples:
❤ Heart rate
🫁 Airway activity
🍽 Digestion
👁 Pupil size
💦 Sweating
Think of it as your body's automatic control system.
The ANS has two main divisions:
1. Sympathetic = FIGHT OR FLIGHT 🚨
Your body prepares to respond to stress, danger or action.
Heart rate increases.
Pupils dilate (get bigger).
Digestion slows.
Sweating increases.
Memory trick: Sympathetic = Survival mode.
2. Parasympathetic = REST AND DIGEST 🌿
Your body focuses on resting, digestion and conserving energy.
Heart rate generally decreases.
Pupils constrict (get smaller).
Digestion increases.
Helps your body return to a resting state.
Memory trick: Parasympathetic = Peace and pasta!
2. Compare them side by side
This table is worth learning for your test.
Body function Sympathetic 🚨 Parasympathetic 🌿
Heart Increases heart rate Generally decreases heart rate
Pupils Dilate — bigger Constrict — smaller
Digestion Decreases activity Increases activity
Saliva Usually reduces watery secretion Promotes watery saliva
Bladder Generally promotes urine storage Promotes urination
Important: These are the typical effects. Some organs have more complex control, but this table is a useful foundation.
3. Imagine this real-life example
You're walking home and a dog suddenly barks and runs toward you. 😱
Step 1: Sympathetic activates
Your heart beats faster to help prepare your body for action.
Step 2: Pupils dilate
Your eyes let in more light.
Step 3: The danger passes
Parasympathetic activity helps your body settle back toward its resting state.
4. A little extra: somatic vs autonomic
Your notes cover the nervous system, so make sure you know this distinction too.
Somatic nervous system: controls skeletal muscle movement and carries conscious sensory information.
Autonomic nervous system: regulates involuntary functions, including the activity of cardiac muscle, smooth muscle and glands.
Memory trick:
Somatic = skeletal movement.
Autonomic = automatic functions.
The 4 lobes of the brain
Think of your brain as having 4 main neighbourhoods, each with a different job.
1. Frontal lobe — THE BOSS
At the front of your brain.
Planning, thinking and decision-making
Personality and impulse control
Voluntary movement
Producing speech (Broca’s area, usually left side)
Memory trick: FRONT = future plans.
2. Parietal lobe — THE FEELER
Near the top, behind the frontal lobe.
Processes touch, pressure, pain and temperature
Helps you understand where your body is in space
Memory trick: PARietal = PRESSURE.
3. Temporal lobe — THE LISTENER
At the sides, near your temples.
Hearing and processing sounds
Important for memory
Understanding language (Wernicke’s area, usually left side)
Memory trick: TEMPLES = TEMporal = sounds.
4. Occipital lobe — THE WATCHER
At the back of your brain.
- Processes visual information — what you see
Memory trick: OCCIPITAL = OPTICAL (vision).
The parts of a neuron
A neuron is a nerve cell that carries information around the body.
Remember the 5 main parts
1. Dendrites = RECEIVE
Receive signals from other cells.
2. Cell body (soma) = CONTROL CENTRE
Contains the nucleus and keeps the neuron functioning.
3. Axon = SENDS
Carries the electrical impulse away from the cell body.
4. Myelin sheath = INSULATION
Wraps around many axons and helps impulses travel faster.
5. Axon terminals = PASS IT ON
Release neurotransmitters to communicate with the next cell.
⚡ The direction of the signal
Dendrites
Receive
Cell body
Processes information
Axon
Carries the impulse
Axon terminals
Communicate with the next cell
Memory trick: Dendrites Detect → Cell body Decides → Axon Away → Terminals Transfer.