Gray's anatomy, introductory chapter

Introduction

   THE TERM human anatomy comprises a consideration of the various structures which make up the human organism. In a restricted sense it deals merely with the parts which form the fully developed individual and which can be rendered evident to the naked eye by various methods of dissection. Regarded from such a standpoint it may be studied by two methods: (1) the various structures may be separately considered—systematic anatomy; or (2) the organs and tissues may be studied in relation to one another—topographical or regional anatomy.

    It is, however, of much advantage to add to the facts ascertained by naked-eye dissection those obtained by the use of the microscope. This introduces two fields of investigation, viz., the study of the minute structure of the various component parts of the body—histology—and the study of the human organism in its immature condition, i. e., the various stages of its intrauterine development from the fertilized ovum up to the period when it assumes an independent existence—embryology. Owing to the difficulty of obtaining material illustrating all the stages of this early development, gaps must be filled up by observations on the development of lower forms—comparative embryology, or by a consideration of adult forms in the line of human ancestry—comparative anatomy. The direct application of the facts of human anatomy to the various pathological conditions which may occur constitutes the subject of applied anatomy. Finally, the appreciation of structures on or immediately underlying the surface of the body is frequently made the subject of special study—surface anatomy.

SYSTEMATIC ANATOMY.—The various systems of which the human body is composed are grouped under the following headings:

Osteology—the bony system or skeleton.

Syndesmology—the articulations or joints.

Myology—the muscles. With the description of the muscles it is convenient to include that of the fasciæ which are so intimately connected with them.

Angiology—the vascular system, comprising the heart, bloodvessels, lymphatic vessels, and lymph glands.

Neurology—the nervous system. The organs of sense may be included in this system.

Splanchnology—the visceral system. Topographically the viscera form two groups, viz., the thoracic viscera and the abdomino-pelvic viscera. The heart, a thoracic viscus, is best considered with the vascular system. The rest of the viscera may be grouped according to their functions: (a) the respiratory apparatus; (b) the digestive apparatus; and (c) the urogenital apparatus.Strictly speaking, the third subgroup should include only such components of the urogenital apparatus as are included within the abdomino-pelvic cavity, but it is convenient to study under this heading certain parts which lie in relation to the surface of the body, e. g., the testes and the external organs of generation.

For descriptive purposes the body is supposed to be in the erect posture, with the arms hanging by the sides and the palms of the hands directed forward. The median plane is a vertical antero-posterior plane, passing through the center of the trunk. This plane will pass approximately through the sagittal suture of the skull, and hence any plane parallel to it is termed a sagittal plane. A vertical plane at right angles to the median plane passes, roughly speaking, through the central part of the coronal suture or through a line parallel to it; such a plane is known as afrontal plane or sometimes as a coronal plane. A plane at right angles to both the median and frontal planes is termed a transverse plane.

    The terms anterior or ventral, and posterior or dorsal, are employed to indicate the relation of parts to the front or back of the body or limbs, and the terms superior or cephalic, andinferior or caudal, to indicate the relative levels of different structures; structures nearer to or farther from the median plane are referred to as medial or lateral respectively.

The terms superficial and deep are strictly confined to descriptions of the relative depth from the surface of the various structures; external and internal are reserved almost entirely for describing the walls of cavities or of hollow viscera. In the case of the limbs the words proximal and distal refer to the relative distance from the attached end of the limb.

Gray's anatomy powerpoint

Brain Presentation

Article on anatomy of the brain

The Human brain is the most highly structured system in the known universe. It controls a plethora of bodily functions; processing sensory information; regulating biochemical processes; coordinating movement and of course, providing us the ability of higher thought/perception. There are three primary areas of the human brain:
• The hindbrain
• The midbrain
• The prosencephalon
Hindbrain
The hindbrain includes the brain stem and cerebellum and controls a number of of functions. It is situated in the cranial cavity.
One essential organ that composes the rhombencephalon is the medulla. The medulla oblongata is directly above the spinal cord and is so essential to life that diseases disturbing it are often fatal.
An additional area is the cerebellum. This section is sometimes called the “little brain”. It looks different to the rest of the brain. It has a surface of densely folded gray matter. It is mainly concerned with movement.
The Pons measures roughly 2cm in length and is situated between the mesencephalon and the medulla. It is composed of nuclei that have significant involvment with sleep, respiration, swallowing, bladder control, hearing, equilibrium, taste, eye movement, facial expressions, facial sensation, and posture.
Midbrain
The Midbrain/Mesencephalon is above the Pons and below the cerebral hemispheres. The rear region of the mesencephalon is often called the tectum, it is significantly responsible for reflexes in relation to auditory processes and sight (e.g. the eye movement, pupil size, lens shape). The anterior section of the mesencephalon is referred to as the tegmentum, it is in essence a highly structured interconnected network of nerves accountable for unconscious homeostatic and reflexive pathways.
Forebrain
The Forebrain is above both the hindbrain and the midbrain as well as being the most ventral. It has central roles in the following actions:
 Mastication
 Directs sensory impulses through the body
 Equilibrium
 Vision
 Eye movement
 Facial sensation
 Hearing
 Phonation
 Intelligence
 Memory
 Personality
 Respiration
 Salivation
 Swallowing
 Smell
 Taste

The Forebrain is split into 2 central structures:

 Telencephalon

The neocortex is the folded outer region of the brain, in humans it is between 0.5cm deep. It has the highest levels of non- insulated grey matter of any section of the brain. The cortex forms folded protrusions (thus significantly expanding the structure without expanding the volume) called gyri; so much so that more than 75% of the brain lie in these crevices (known as sucli).
The Frontal lobe is the most forward structure of the lobes and is additionally superior to the temporal lobe. This structure of the brain is connected with some of of the the most crucial traits associated with personality (e.g ability to know future results of action taken), learning, impulse control, and priority of actions. It is host to most of the brain’s dopamine receptors (these are the major way through which learning is rewarded).

The temporal lobes are inferior to the frontal and parietal lobe and anterior to the occipital lobe. Studies imply they are the essential portion of the brain involved in declarative memory; damage to the temporal lobes can result in an inability to form memory after the point of damage (anterograde amnesia). They contain the hippocampus (long-term memory) and are concerned auditory and higher visual perception (e.g. facial recognition).

The parietal lobe is anterior of the occipital lobe, behind the frontal lobe and superior of the temporal lobes. The border between the frontal lobe and the parietal lobe is marked by the central sulcus. The border between the occipital lobe and the parietal lobe is marked by the parieto-occipito sulcus and the border between the temporal lobe and the parietal lobe is marked by the lateral sulcus. The parietal lobe coordinates information from multiple senses in order to establish spatial orientation.
The Occipital lobe is the most posterior of all the main lobes of the brain. Anatomically this part contains most of the visual cortex (Brodmann area 17) and damage to the occipital lobes results in essential homonomous vision loss (i.e. the effect is the same in both eyes). The occipital lobes are where shape, colour, and like the temporal lobes, facial recognition take place. Projections from the occipital lobe to the superior temporal-parietal area are critical for perceiving motion of objects.

The basal ganglia are a portion of the corpus striatum and are in essence a set of interconnected nuclei within the brain. Messages from the cerebrum passes to the basal ganglia where it is processed and then relayed back through the thalamus. There are a great deal of connections and pathways within and although the basal ganglia have long been known to be involved in motor function; studies show this is not there sole function, though the exact action in relation to behaviour control have yet to be properly established. Evidence suggests that during learning, basal ganglia and medial temporal lobe memory systems are activated simultaneously and that in some learning situations competitive interference exists between these two systems. One theory suggests the basal ganglia decides which out of a number of possible actions the cortex may be planning, actually gets executed. Fitting this with idea that dopamine is used as a reward system for learning.

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Basic/GCSE anatomy of the nervous system

The nervous system is vital to the body in lots of ways. It allows us to detect changes in our environment but additionally the ability to take action. The nervous system is divided into two main sections:

1.The central nervous system-The spinal chord and the brain

2. The peripheral nervous system-All the other neurons that connect to the central nervous system

Special cells called receptors are used by the human body to determine stimuli (changes in the environment) and transmit information to the brain in the form of electrical impulses. Receptors are most commonly located at special organs, these include:

Eye: Receptors here are perceive changes in light

Skin: Receptors here are sense changes in pressure and
temperature

Tongue: Receptors here are determine chemicals in food

Ears: Receptors here are determine changes in sound levels and changes in position (so we can keep our balance)

Nose: Receptors here are responsible for changes in chemicals in the air

When a receptor senses forms of stimuli it sends the information as an electrical signal down nerves (neurons). The brain is then able to gather information about changes in the environment and co-ordinate a response. This response is more rapid and frequently involves effectors.

Effectors

Effectors are muscles/glands that the brain sends commands to via neurones. Any mobile part of the body is an effector as are internal glands: a muscle used to lift your leg up is an effector; a muscle that controls the eye lid is an effector; a gland that releases a hormone into the cardiovascular system is an effector.

Reflex

Most of the time when a receptor senses stimuli it causes an electrical message to travel down the sensory neurone to the central nervous system. Here the brain organises a response (thinking time) and another impulse is sent down down the motor nerve.This in turn sends an electrical message to an effector and the effector produces a response:

Stimuli->Receptor->Sensory neuron->CNS->Motor neuron->Effector->Response

In some cases this response time is too slow and this would lead us to get injured. At these times the system does not include the CNS to speed up the reaction: a receptor detects stimuli and an electrical message goes down the sensory nerve. At this point it sends an electrical impulse down a relay neuron which bypasses the brain and communicates directly with a motor nerve which causes an effector to produce a reaction:
Stimuli->Receptor->Sensory neuron->Relay neuron->Motor neuron-Effector->Response
Though a relay neuron is part of the CNS, this is more quickly as it does not include the thinking time.

Neurone Structure

Nerves are a type of cell that is capable of transmitting electrical impulses. Nerves are involved in the whole nervous system. Without them we couldn't think or move! There are three main types of nerve:

1.Sensory neurons
2.Relay neurons
3.Motor neurons

Despite these three different nerves having different places within the nervous system, they share some central features:

Axon: This is what an electrical impulse travels down

Myelin Sheathe: This insulates the Axon and quickens up the electrical impulse.

Dendrites: These overlap with other neuron dendrites at junctions called synapses. This is where neurones communicate with each other.

Nerve Synapses

Synapses are the area where nerve cells (neurons) pass impulses between each other. The impulse travels down the axon. At the Dendrites (dendrons) it comes to a synapse. The message causes a neurotransmitter to be released across the neurone synapse. The neurotransmitter causes the next nerve cell to pass an impulse along its axon. In this way a nervous impulse can travel all over the body, controlling all sorts of processes and responses.