HUMAN BRANE

The cerebrum The cerebellum The hypothalamus The pituitary gland The medulla oblongata

Largest part of the brain (~80% of brain mass) Responsible for conscious activities: vision, hearing, speech, thinking, and memory Divided into two cerebral hemispheres connected by the corpus callosum Right hemisphere controls left side of body and vice versa Outer layer = cerebral cortex (grey matter) containing neurone cell bodies Cortex is highly folded → increases surface area → more neurones and connections for complex behaviour Beneath cortex is white matter containing myelinated axons

Located in the lower middle part of the brain, just above and connected to the pituitary gland Monitors the composition of blood and maintains homeostasis by releasing hormones or stimulating the pituitary gland Main functions: Thermoregulation: monitors blood temperature and initiates responses if too hot or cold Osmoregulation: detects blood water concentration and stimulates release of ADH from the posterior pituitary; also triggers thirst Digestive regulation: controls gut enzyme secretion and peristalsis; triggers hunger if nutrients are low Endocrine control: releases hormones that regulate pituitary hormone secretion (affecting metabolism, growth, puberty, sleep, mood)

Located at the base of the brain below the hypothalamus Known as the “master gland” because it produces hormones that control other endocrine glands Secretes hormones that directly regulate body processes or stimulate other glands to release hormones Two sections: Anterior pituitary: produces and releases hormones Posterior pituitary: stores and releases hormones made by the hypothalamus (e.g. ADH and oxytocin)

Located below the cerebrum at the back of the brain Responsible for motor coordination Coordinates balance, posture, and smooth movement Balance requires coordination between the eyes, semicircular canals in the ears, and muscles Functions subconsciously (involuntary control)

Located at the base of the brain where it connects to the spinal cord Controls involuntary (autonomic) functions Contains three centres: Cardiac centre: controls heart rate Vasomotor centre: controls blood pressure by regulating contraction of smooth muscle in arteriole walls Respiratory centre: controls breathing rate (has inspiratory and expiratory centres)

Involuntary (automatic)

Voluntary (conscious control)

Stimulus: stretch of quadriceps muscle Receptor: stretch receptors in quadriceps Sensory neurone: carries impulse to spinal cord Coordinator: spinal cord Motor neurone: carries impulse to quadriceps Effector: quadriceps muscle Response: quadriceps contracts → leg straightens (kick)

Stimulus: irritation or drying of the cornea Sensory neurone: impulses travel via the trigeminal nerve to the medulla in the brain Coordinator: medulla Relay neurones: transmit impulses to motor neurones Effectors: Superior levator palpebrae muscle (lowers upper eyelid) Orbicularis oculi muscle (pulls eyelids together) Response: eyelids close (blink) Key point: Reflex passes through the brain but bypasses conscious decision-making, so it is rapid and automatic.

The acceleratory centre, which causes the heart to speed up The inhibitory centre, which causes the heart to slow down Both centres are connected to the sinoatrial node (SAN) by nerves

The acceleratory centre in the medulla oblongata increases heart rate When activated, it sends impulses along sympathetic neurones to the SAN (sinoatrial node) Noradrenaline is released at the synapse with the SAN Noradrenaline increases the frequency of electrical impulses produced by the SAN This results in an increased heart rate

The inhibitory centre sends impulses along parasympathetic neurones to the SAN (sinoatrial node). Acetylcholine is released at the synapse with the SAN. Acetylcholine reduces the frequency of electrical waves produced by the SAN. This decreases heart rate, bringing it back towards the resting rate.

During exercise, internal conditions change: CO₂ concentration increases Blood pressure initially falls due to dilation of muscle arterioles. These changes are detected by chemoreceptors and pressure receptors in the aorta and carotid arteries. The receptors send nerve impulses to the acceleratory and inhibitory centres in the medulla. The frequency of impulses determines the response: Low frequency impulses → activate inhibitory centre → heart rate decreases High frequency impulses → activate acceleratory centre → heart rate increases.

A gland is a group of cells that produces and releases one or more substances (a process known as secretion)

Adrenaline and noradrenaline both released from the adrenal gland Thyroxine produced by thyroid gland