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The divisions of the nervous system: central andperipheral (somatic and autonomic)
The human nervous system is a collection of neurons across
the body that detects information from the environment and
processes this, then directs the body to take action via the
muscles and/or glands. It is split into the Central nervous
system (CNS) and the Peripheral nervous system (PNS).
● The CNS is responsible for our complex processing. It
consists of the brain (the centre of all conscious and
most unconscious processing) and the spinal cord
(this receives and transmits information).
● The PNS is the portion of the nervous system that is
outside the brain and spinal cord. The primary
function of the peripheral nervous system is to
connect the brain and spinal cord to the rest of the
body and the external environment.
★ The peripheral nervous system is split into the
somatic and autonomic nervous systems
★ Somatic Nervous System (SNS) connects the central nervous system with the senses
and is composed of sensory nerve pathways bring information to the CNS from sensory
receptors, dealing with touch, pain, pressure, temperature etc, and motor nerve
pathways which control bodily movement by carrying instructions towards muscles
● Autonomic Nervous System (ANS) controls bodily arousal (how ‘excited’ or relaxed we
are), body temperature, homeostasis, heart rate and blood pressure. It is composed of
the sympathetic and parasympathetic nervous systems. the sympathetic ANS is involved
in preparing the body for fight or flight, so causes increased arousal (e.g. increase in
heart rate and blood pressure, pupil dilation, reduction in digestion and salivation)and
the parasympathetic ANS is used to return our body back to its normal state after the
fight or flight response, so leads to decreased arousal.
Under normal conditions there is a balance between the sympathetic and parasympathetic
systems in order to maintain homeostasis.
CENTRAL NERVOUS SYSTEM (brain & spinal cord)
Similarities:
● The brainstem and spinal cord both control involuntary processes (e.g. the brain stem
controls breathing and the spinal cord controls involuntary reflexes).
Differences:
● The brain provides conscious awareness and allows for higher-order thinking, while the
spinal cord allows for simple reflex responses.
, ● The brain consists of multiple regions responsible for different functions, whereas the
spinal cord has one main function.
PERIPHERAL NERVOUS SYSTEM (somatic/autonomic & sympathetic/parasympathetic)
Similarities:
● The sympathetic nervous system (part of the autonomic nervous system) and the
somatic nervous system respond to external stimuli. The sympathetic nervous system
responds to external stimuli by preparing the body for fight or flight and the somatic
nervous system responds to external stimuli by carrying information from sensory
receptors to the spinal cord and brain.
Differences:
● The autonomic nervous system consists of two sub-components, whereas the somatic
nervous system only has one.
● The somatic nervous system has sensory and motor pathways, whereas the autonomic
nervous system only has motor pathways.
● The autonomic nervous system controls internal organs and glands, while the somatic
nervous system controls muscles and movement.
The function of the endocrine system: glands and hormones
The Endocrine system is a series of glands located across the
body which release hormones. These enter the bloodstream and
send messages to other parts of the body. This is slower than the
nervous system but can have stronger and longer lasting effects.
● The Hypothalamus is connected to the pituitary gland and is
responsible for stimulating or controlling the release of
hormones from the pituitary gland. Therefore, the
hypothalamus is the control system which regulates the
endocrine system.
● The pituitary gland is sometimes known as the master gland
because the hormones released by the pituitary gland
control and stimulate the release of hormones from
other glands in the endocrine system. The pituitary
gland is also divided into the anterior (front) and
posterior (rear) lobes (see right), which release
different hormones. A key hormone released from the
posterior lobe is oxytocin (often referred to as the ‘love
hormone’) which is responsible for uterus contractions
during childbirth. A key hormone released from the
anterior lobe is adrenocortical trophic hormone (ACTH)
which stimulates the adrenal cortex and the release of
cortisol, during the stress response.
, ● The main hormone released from the pineal gland is melatonin, which is responsible for
important biological rhythms, including the sleep-wake cycle.
● The thyroid gland releases thyroxine which is responsible for regulating metabolism.
People who have a fast metabolism typically struggle to put on weight, as metabolism is
involved in the chemical process of converting food into energy.
● The Pancreas releases insulin to lower blood glucose levels and releases glucagon to
raise blood glucose levels.
● The adrenal gland is divided into two parts, the adrenal medulla and the adrenal cortex.
The adrenal medulla is responsible for releasing adrenaline and noradrenaline, which
play a key role in the fight or flight response. The adrenal cortex releases cortisol, which
stimulates the release of glucose to provide the body with energy while suppressing the
immune system.
● Males and females have different sex organs, and in males the testes release
androgens, which include the main hormone testosterone. Testosterone is responsible
for the development of male sex characteristics during puberty while also promoting
muscle growth. In females, the ovaries release oestrogen which controls the regulation
of the female reproductive system, including the menstrual cycle and pregnancy.
The fight or flight response including the role of adrenaline
● Stress is experienced when a person’s perceived environmental, social and/or physical
demands exceed their perceived ability to cope.
● The stress response (otherwise known as the ‘fight or flight’ response) is hard-wired into
our brains and represents an evolutionary adaptation designed to increase an
organism’s chances of survival in life-threatening situations.
The fight or flight response involves two major systems:
● The Sympathomedullary Pathway – deals with acute (short-term, immediate) stressors
such as personal attack.
● The Hypothalamic Pituitary-Adrenal System – deals with chronic (long-term, on-going)
stressors such as a stressful job.
The Sympathomedullary Pathway (SAM)
● The hypothalamus also activates the adrenal medulla. The adrenal medulla is part of the
autonomic nervous system (ANS).
● The ANS is the part of the peripheral nervous system that acts as a control system,
maintaining homeostasis in the body. These activities are generally performed without
conscious control.
● The adrenal medulla secretes the hormone adrenaline. This hormone gets the body
ready for a fight or flight response. Physiological reaction includes increased heart rate.
● Adrenaline lead to the arousal of the sympathetic nervous system and reduced activity in
the parasympathetic nervous system.
● Adrenaline creates changes in the body such as decreases (in digestion) and increases
(sweating, increased pulse and blood pressure).
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